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< 
THE INTERNATIONAL SCIENTIFIC SERIES 



ON THE SENSES 

INSTINCTS, AND INTELLIGENCE 

OF ANIMALS 



WITH SPECIAL REFERENCE TO INSECTS 



BY 

Sir JOHN LUBBOCK, Bart. 

M.P., F.R. S., D.C.L., LL.D. 

AUTHOR OF "ANTS, BEES, AND WASPS;" "PREHISTORIC TIMES," ETC. 



WITH OVER ONE HUNDRED ILLUSTRATIONS 



NEW YOKK 

D, APPLETON AND COMPANY 

1888 






Transfer 
engineers School Uby. 
June 29,1931 



PREFACE. 



In the present volume I have collected together some 
of my recent observations on the senses and intelli- 
gence of animals, and especially of insects. 

While attempting to understand the manners and 
customs, habits and behaviour, of animals, as well as for 
the purpose of devising test experiments, I have found 
it necessary to make myself acquainted as far as possible 
with the mechanism of the senses, and the organs by 
means of which sensations are transmitted. With this 
object I had to look up a great number of memoirs, in 
various languages, and scattered through many different 
periodicals ; and it seemed to me that it might be inte- 
resting, and save others some of the labour I had to 
undergo myself, if I were to bring together the notes 
I had made, and give a list of the principal memoirs 
consulted. I have accordingly attempted to give, very 
briefly, some idea of the organs of sense, commencing 
in each case with those of man himself. 



VI PKEFACE. 

Mr. John Evans, Dr. M. Foster, and my brother, Dr. 
Lubbock, have been so kind as to read through the 
proofs, and I have to thank them for many valuable 
suggestions. Lord Eayleigh also has been so good as 
to look at the chapters on Hearing. 

High Elms, Down, Kent, 



CONTENTS. 



CHAPTEK I. 

PAGE 

Introductory remarks — Difficulty of the subject — The life of a 
cell — Possible modes of origin of sense-organs — Origin of 
eye and ear — The sense of touch — The organs of touch — 
Nerves of touch — Sense of temperature — Cold points — Heat 
points — Pressure-points — Organs of touch among lower 
animals — Medusae — Annelides — Mollusca — Crustacea — In- 
sects — Sense-hairs — Tactile hairs ... ,,, ... 1 

CHAPTER II. 

The sense of taste — Taste-organs of man — Mammalia — Birds — 
Reptiles — Taste-organs of the lower animals — Crustacea — 
Insects — Sense of taste in insects — Organs of taste in 
insects — The bee — Humble bee — Wasp — Fly — Individual 
differences ... ... ... ... ... ... 19 

CHAPTER III. 

The sense of smell — Protozoa and Coelenterata — Worms — Mollusca 
— Insects— Seat of the sense of smell — Different theories as 
to the seat of the sense of smell in Insects — Experiments 
with Dinetus — Hydaticus — Silpha — Stag-beetle — Ants — 
Seat of the sense of smell partly in the palpi, partly in 
antennae — Organs of smell — Leydig's olfactory cones — 
Organs of smell in Crustacea — Centipedes — Olfactory 
cones in insects — Olfactory hairs — Olfactory pits — Ol- 
factory organs of fly — Antenna of Ichneumon — Olfactory 
organs of wasp — Antennal organs of insects — Comrjlex 
structure of the antennae — Various uses of antennae ... 32 



Viil CONTENTS. 



CHAPTER IV. 



The sense of hearing — Organs of sound — Mollusca — Crustacea — 
Insects — Locusts — Grasshoppers — Crickets — Cicadas — 
Beetles — The bombardier beetle — Paussus — Death-watch — 
Burying beetles — Weevils — Cockchafers — Variety of organs 
of sound among beetles — Diptera — Hymenoptera — Ants — 
Bees — Sounds produced in flight — Power of varying sound 
— Butterflies — Moths — Centipedes — Spiders — Power of hear- 
ing in insects — Sense of hearing in insects ,,, ... 60 

CHAPTER V. 

The organs of hearing — Structure of the human ear — The organ 
of Corti — Mode of action of auditory organs — Organs of 
hearing in the lower animals — Medusse — Auditory hairs — ■ 
Mollusca — Annelides — Crustacea — Use of grains of sand as 
otolithes — Ear in tail of Mysis — Mode of hearing — Organs 
of hearing in insects — Seat of the sense of hearing in insects 
— Different seats of organs of sense — Ears in legs of crickets 
— Ear of grasshoppers — Structure of ear — Auditory rods — 
Ear of locusts — Peculiar structure in leg of ant — Origin of 
ear — Ear of fly — Peculiar sense-organs— Auditory rods in 
beetles — Position of auditory rods — Chordotonal organs — 
Auditory hairs of antennae of gnat — Sympathetic vibrations 
— Organs of hearing in various parts of body ... ... 77 

CHAPTER VI. 

The sense of sight — Three possible modes of sight—Different 
forms of eye — The vertebrate eye— Structure of the eye — 
The retina — The rods and cones — The blind spot in the eye 
— Inversion of the rods — The pineal gland — The rudimentary 
median eye — The median vertebrate eye — The organs of 
vision in the lower animals— Color-spots — Echinoderms — 
Worms — Molluscs— Cuttle-fish — Compound eyes in Molluscs 
— Area— Spondylus — Pecten — Onchidium — Sense-organs of 
Chiton 118 

CHAPTER VII. 

The organs of vision in Insects and Crustacea — Ocelli — Compound 
eyes — Cornea — Crystalline cones — Retinula — Pigment — 
Different forms of eyes — Structure of the optic lobes — Eyes 



CONTENTS. IX 



of Crustacea — Structure of eye — My sis — Corycseus— Copilia 
— Calanella — Limulus — ScorpioDS — Light-organs of Eu- 
phausia — Mode of vision by compound eyes — Mtiller's theory 
of Mosaic vision — Images thrown by the cornea — Objections 
to other theories— Position of the image— Absence of power 
of accommodation — Absence of retina — Summary — On the 
power of vision in insects — Experiments on vision of insects 
— On the function of ocelli — Difficulty of subject — Experi- 
ments—Short sight of ocelli — Ocelli of cave-dwelling spiders 
— Probable function of ocelli ... ... ... ••• 146 

CHAPTER VIII. 

On problematical organs of sense — Muciferous canals of fish — 
Deep-sea fish — Light-organs — Living lamps — Problematical 
organs in lower animals — Medusae — Insects — Crustacea — 
Difficulty of problem — Size of ultimate atoms — The range 
of vision and of hearing — Unknown senses — The unknown 
world ... ... ... ... ... ... 182 

CHAPTER IX. 

On bees and colors— Experiments with colored papers — Dr. 
Miiller's objections — Reply to objections — Preferences of 
bees — The colors of flowers ... ... ... ... 194 

CHAPTER X. 

On the limits of vision of animals — Ants and colors — The 
ultra-violet rays — The limits of vision in ants — Supposed 
perception of light by the general surface of the skin — 
Experiments with hoodwinked ants — Confirmation of my 
experiments on ants — Experiments with Daphnias — Daph- 
nias and colors — Preference for yellowish green — Experi- 
ments — Limits of vision of Daphnias — Perception of 
ultra-violet rays — Objections of M. Merejkowski — Suggestion 
that Daphnias perceive brightness, but not color — Further 
experiments — Evidence that Daphnias perceive differences 
of color .„ ... ... ... ... „. 202 

CHAPTER XL 

On recognition among ants — Experiments with intoxicated ants 
— Evidence against recognition by means of a sign or pass- 
word — Experiments with ants removed from the nest as 



CONTENTS. 



PAGE 



pupse and subsequently restored — Experiments with drowned 
ants — Recognition after a year and nine months — Supposed 
recognition by scent — Recognition by means of the antennae 232 

CHAPTER XII. 

On the instincts of solitary wasps and bees — Instinct of render- 
ing victims insensible — Origin of instincts — Habits not 
invariable — Change of instincts — Bembex — Odynerus — Am- 
mophila — Modifiability of instincts — Differences under 
different circumstances — Origin of the habits of Sphex — 
Race differences — Limitation of instinct — Toleration of para- 
sites — Cases of apparent stupidity — M. Fabre's experiments 
— Limitation of instinct — Instinct and habits— -Inflexibility 
of instinct— Different habits of males and females — Arrange- 
ment of male and female cells — Power of mother to regulate 
the sex of the young ... ... ... ... ... 242 

CHAPTER XIII. 

On the supposed sense of direction — Experiments with bees — 
Whirling bees — Behaviour of bees if taken from home — 
Mode of finding their way — Experiments with ants— Mr. 
Romanes' experiments — No evidence of separate sense 
of direction ... ... ... .., ... ... 262 

CHAPTER XIV. 

On the intelligence of the dog — Education of the deaf and dumb 
— Laura Bridgman — Application of the method followed 
with the deaf and dumb to animals — My dog Van and his 
cards — Use of cards with words on them, " food," il water," 
" tea," etc. — Recognition of the separate cards — Association 
of the card with the object — Realization that bringing a 
card was a request — Attempts to convey ideas — Arithmetical 
powers of animals — Previous observations — Supposed powers 
of counting — Mr. Huggins's experiments — Conclusion ... 272 



LIST OF ILLUSTRATIONS. 



FIGURE PAGE 

1. Diagram to illustrate possible origin of a sense-organ, c, Cuticle; 

A, cellular or hypodermic layer .. . . . . . . 3 

2. Diagram to illustrate possible origin of a sense-organ, c, Cuticle ; 

h, cellular or hypodermic layer .. .. .. .. 3 

3. Diagram to illustrate possible origin of a sense-organ, c, Cuticle ; 

h, hypoderm ; n, nerve . . . . . . . . . . 4 

4. Diagram of further stage in the origin of a sense-organ . . 4 

5. Diagram illustrating a second possible origin of a sense-organ 5 

6. Diagram of further stage in the origin of a sense-organ . . 5 

7. Section through the simple eye of a young Dytiscus larva, h, 

Hypoderm ; I, lens ; o, optic nerve ; g, p, modified hypodermic 
cells ; r, retina . . . . , . . . . . . . . . 6 

8. Auditory vesicle of Ontochis . . . . . . . . . . 6 

9. Pacinian corpuscle, a, Neurilemma; 6, nerve-fibril ; c, capsule ; 

d, peculiar fibres ; e, central cylinder . . . . . . . . 8 

10. Papilla from the surface of the hand, X 350. a, Cone-like body ; 

b, nerve ; c, end of nerve . . . . . . . . . . 8 

11. Portion of the skin of the back of the hand. The centre figure 

represents the arrangement of the hairs ; CP, the cold-points ; 
WP y the warmth-points . . . . . . . . . 10 

12. Half a "cross section through the brain and hinder pair of eyes of 

Nereis cultrifera, 1, Hypoderm ; 2, cuticle ; 3, retina ; 4, 
outer corneal cells ; 5, inner corneal cells ; 6, brain ; 8, 8a, 
two places to which the brain sends large nerves, but where 
the cuticle is unaltered ; g, gelatinous body . . . . 12 

13. Part of upper nerve-ring and tactile epithelium of Lizzia. a, 

Tactile epithelium ; g, ganglionic cell ; nr 1 , upper nerve-ring 12 

14. Diagram of part of the skin of a sea-anemone (Actinia), dz, 

Glandular cell ; nz, nervous cell . . . . . . 13 

15. Anterior part of body of Bohemilla comata. lb, Tactile hair ; 



xii LIST OF ILLUSTKATIONS. 

FIGURE PAGE 

hy, hypoderm ; c, cuticle ; 6, anterior part of brain ; a, eye ; 

ne, nerve-fibrils ; v, anterior blood-vessel . . . . 13 

16. Diagrammatic section through a papilla of touch of Onchidium. 

a', a", two layers of the cuticle ; a, biconvex thickened portion 
of the cuticle ; 6, enlarged epithelial cells ; &', ordinary epithe- 
lial cells ; c, cellular body ; d, cells ; w, nerve . . . . 14 

17. Diagram of the structure of the soft and some of the hard parts 

in the tegmentum of a shell of a Chiton (Acanthopleura spiniger), 
as seen in a section vertical to the surface, and with the margin 
of the shell bordering on the girdle lying in the direction of 
the left side of the drawing. /, Calcareous cornea ; h, iris ; 
g, lens ; k, pigmented capsule of eye ; n, optic nerve ; r, rods 
of retina ; n', branches of the optic nerve, perforating the cap- 
sule wall, and terminating in b', &', b', ocular sense-organs ; 
p, p, nerves to sense-organ ; m, body of sense-organ cut across ; 
a, p, fusiform body of sense-organ entire ; a, obconical termi- 
nation of sense-organ ; e, nerve given off by one sense-organ 
to another, b" . . . . . . . . . . 15 

18. Diagram of forms of hairs in insects, a, Ordinary surface hair; 

o, plumose natatory hair ; c, hair of touch ; d, auditory hair ; 

e, olfactory hair ; /, taste hair ; n, nerve hair . . . . 16 

19. Part of the proboscis of a fly (Musca). n, nerve ; g, ganglionic 

swellings; s, tactile hairs or rods ; c, cuticle . . . . 17 

20. Right half of eighth segment of the body of the larva of a gnat 

(Corethra plumicomis). EG, Ganglion ; N, nerve ; g, auditory 
ganglion; gb, auditory ligament; Ch, auditory rods ; a, auditory 
nerve ; e, attachment of auditory organ to the skin ; 6, attach- 
ment of auditory ligament ; hn, hn', termination of skin-nerve ; 
tb, plumose tactile hair ; h, simple hair ; tg, ganglion of tactile 
hair; Im, longitudinal muscle .. .. .. .. ..18 

21. Taste-buds of the rabbit, X 450 20 

22. a, Isolated taste-cells from the mouth of a rabbit ; b, two cover- 

cells and a taste-cell in their natural position, x 600 . . 20 

23. Termination of the nerves of taste in the frog, showing the 

ramifications of the nerve-fibres and their connections with the 
cells of taste, X 600 21 

24. Inner layer of skin of the proboscis of Asterope Candida, X 400. 

a, Cuticle ; 6, terminal (nerve) organs ; c, ganglionic cells ; 

d, longitudinal muscle ; e, transverse muscle . . . . 22 

25. Taste-organ of the bee. B, Horny ridge ; B, B, sensory pits ; 

(7, C, skin of the mouth ; Z, muscular fibres ; A, A, muscular 
fibres ; S, S', a b c d e f, section of the skin of oesophagus . . 26 



LIST OF ILLUSTKATIONS. xiil 

FIGURR PAGE 

26. Shows three of Wolffs cups, each with a central hair, a chitinous 

ring, and a double ganglionic swelling terminating in a nerve- 
fibre, X 500 times. R, E\ Sensory pits and hairs ; G, G, 
ganglionic swelling of nerve .. . . .. .. ..27 

27. Under side of left maxilla of Vespa. Gm, Taste-cups ; Shm, pro- 

tecting hairs ; Tb, tactile hairs ; Mt, base of maxillary palpus 28 

28. Section through a taste-cup. SK, Supporting cone; X, nerve; 

SZ, sense-cell . . . . . . . . . . . . 28 

29. Tip of the proboscis in the hive bee (Apis), X 140. L, Terminal 

ladle ; Gs, taste-hairs ; Sh, guard-hairs ; Bb, hooked hairs . . 29 

30. Organ of taste of fly {Musca vomitorid). gn, Nerve ; gg, ganglion ; 

ax, axe-cylinder ; gc, terminal cylinder ; gk, terminal cone . . 30 

31. Epithelial and (B) olfactory cells of man. . . . . . 33 

32. Cells from the olfactory region of a proteus (after Strieker), a, 

Epithelial cells ; b, the apparent processes ; c, olfactory cells. 

A, ciliae . . . . . . . . . . . . . . . . 33 

33. Section through the head segment of Polyophthalmus, x 300. 

Imd, muscle ; bo, cup-shaped organ ; cu, cuticle ; hp, hypo- 
derm ; Imd, longitudinal dorsal muscle ; n, peripheral nerve ; 

b, cerebral ganglion ; cz, commissure of brain ; mb, membrane ; 
pmg, pigment cells ; hpdz, unicellular glands in the hypoderm ; 

gn, brain ; k, nuclei in the brain . . . . . . 34 

34. Antenna of Pontella Bairdii (Lubbock) . . . . . . 47 

35. Terminal segments of one of the smaller antenna? of the water- 

woodlouse (Asellus aquaticus), X 500. a, Ordinary hairs (not 
connected with a nerve) ; b, hairs of touch (with a nerve at 
the base) ; c, special cylinders (olfactory cylinders) . . 48 

36. Tip of the antenna of a centipede (Julus terrestris), X 600. At 

the apex are four olfactory cylinders, a few of which are also 
seen on the following segment, among the ordinary hairs . . 49 

37. End of a palpus of Staphylinus erythropterus, X 600. a, Olfac- 

tory pit . . . , . . . . . . . . . . 50 

38. Part of antenna of Callianassa subterranea. b, Olfactory hairs ; 

g, peculiar curved hairs . . . . . . ., . . 50 

39. Terminations of olfactory hairs of Crustacea, a, Of larva of a 

Palcemon ; 6, of a Pagurus ; c, of a Pinnotheres ; d, of a Squilla ; 

e, of a Pontonia . . . . . . . . . . . . 51 

40. Antenna of blowfly, a, Enlarged third segment, showing pits ; 

c, base of the antenna . . . . . . . . . . 53 

41. One segment of the antenna of an Ichneumon . . . . 54 

42. Section through part of the antenna of a wasp, X 430. CH, 
. Chitinous skin ; Z, olfactory cone ; G, .olfactory pit ; TB, tac- 



XIV LIST OF ILLUSTRATIONS. 

FIGURE PAGE 

tile hairs ; H, hypodermic cells ; Jf, the membrane surrounding 
them; K, nuclei of the olfactory cell; JT, remains of the 
earlier upper nucleus ; SK 9 lower circle of rods ; IZS, olfactory 
rod ; GZ, Geisselzelle ; MZ, membrane forming cell ; Jf, mem- 
brane closing the pit . . . . . . . . . . 55 

43. Diagram showing structures on the terminal segment of the 

antennae of insects, a, Chitinous cuticle ; 6, hypodermic layer ; 

c, ordinary hair ; d, tactile hair ; 0, cone ; /, depressed hair, 
lying over g, cup, with rudimentary hair at the base ; A, simple 
cup ; t, champagne-cork-like organ of Forel ; k, flask-like 
organ ; I, papilla, with a rudimentary hair at the apex . . 56 

44. Leg of Stenobothrus pratorum . . . . . . . . 62 

45. Sound-bow of Stenobothrus . . . . . . . . 63 

46. Diagram of human ear. D, Auditory canal ; E, mouth of Eusta- 

chian tube ; cc, tympanic membrane ; B, tympanic cavity ; 0, 
fenestra ovalis ; r, fenestra rotunda ; s, semicircular canals ; 
A, cochlea . . . . . . . . . . . . . . 78 

47. Ossicles of the ear. H, Hammer ; Am, anvil ; Am. k, shorter 

process of the anvil ; Am. I, longer process of the anvil ; S, 
stirrup ; St, long process of the hammer . . . . 78 

48. Section through the ampulla. iV, nerve ; z, terminal cells ; h, 

auditory hairs . . . . . . . . . . . . . . 79 

49. Tympanal wall of the ductus cochlearis, from the dog. Surface 

view from the side of the scala vestibuli, after the removal of 
Reissner's membrane, 20Q. I. Zona denticulata Corti. II. Zona 
pectinata Todd-Bowman : 1, Habenula sulcata Corti ; 2, Ha- 
benula denticulata Corti ; 3, Habenula perforata Kolliker. 
III. Organ of Corti : a, portion of the lamina spiralis ossea 
(the epithelium is wanting) ; b and c, periosteal blood-vessels ; 

d, line of attachment of Reissner's membrane ; e and e t , epi- 
thelium of the crista spiralis ; /, auditory teeth, with the 
interdental furrows; g, g t , large-celled (swollen) epithelium 
of the sulcus spiralis internus, over a certain extent shining 
through the auditory teeth ; from the left side of the pre- 
paration they have been removed ; h, smaller epithelial cells 
near the inner slope of the organ of Corti ; k, openings through 
which the nerves pass ; t, inner hair cells ; l 9 inner pillars ; 
m, their heads ; 0, outer pillars ; w, their heads ; p, lamina 
reticularis ; q, a few mutilated outer hair cells ; r, outer 
epithelium of the ductus cochlearis (Claudius's cells of the 
author's) ; removed at s in order to show the points of attach- 
ment of the outer hair cells . . , . , . . , 80 



LIST OF ILLUSTEATIONS. XV 

FIGURE PAGE 

50. Eutima gigas . . . » , • . . . . , . . . 83 

51. Auditory organ of Ontorchis Gegenbauri . . . . . . 84 

52. Auditory organ of Phialidium. d [ , Epithelium of the upper 

surface of the velum; d 2 , epithelium of the under surface of 
the velum ; hh, auditory hairs ; h, auditory cells ; np, nervous 
cushion ; nr', nerve-ring ; r, circular canal at the edge of the 
velum . . . . . . . . . . . . . . . . 85 

53. Auditory organ of Rhopalonema, still showing a small orifice. 

kk, Modified tentacle ; o, auditory organ . . . . . . 85 

54. Sense-organ of Pelagia. o, Group of crystals , sk, sense-organ ; 

sf, fold of the skin ; ga, gastro-vascular channel . . . . 86 

55. Auditory organ of Unio. a, Nerve ; b, cells ; c, ciliae ; d, otolithe 87 

56. Auditory organ of Pterotrachea Friderioi, Na, Auditory nerve ; 

c, central cells ; d, supporting plate ; b, outer circle of audi- 
tory cells ; a, ciliated cells . . . . . , . . . . 87 

57. Base of right antennule of lobster (Astacus marinus). a, Orifice ; 

s, sac . . . . . . . . . . . . . . . . 88 

58. Interior of auditory sac of lobster, a, Orifice ; h, auditory hairs 88 

59. Part of wall of auditory sac of lobster (Astacus m r trinus). a, 

Thickened bars in the membrane of the sac ; 77, first row of 
auditory hairs ; 77', second row of auditory hairs ; 77", third row 
of auditory hairs ; 77'", fourth row of auditory hairs ; e, grains 
of sand, serving as otolithes . . . . . . . . . . 89 

60. Auditory hair of crab (Carcinus masnus), X 500. a, Skin ; c, 

nerve ; h, delicate intermediary membrane or hinge . . . . 92 

61. Mysis . . . . . . . . . . . . . . , , 92 

62. Tail of Mysis vulgaris, showing the auditory organ . . . . 93 

63. Part of the leg of a grasshopper (Gryllus). 0, t, n, b, tympanum 98 

64. Section through the tibia (leg) of a Meconema, x about 150. 

tr, tr, The two tracheae ; ar, the auditory rod . . . . 102 

65. The tracheas and nerve-end organs from the tibia (leg) of a 

grasshopper (Ephippigera vitium). EBI 9 Terminal vesicles of 
Siebold's organ ; HT, hinder tympanum ; Sp, space between 
the trachea ; hTr, hinder branch of the trachea ; &#", nerves 
of the organ of Siebold ; go, supra-tympanal ganglion ; Gr, 
group of vesicles of the organ of Siebold ; vN, connecting 
nerve-fibrils between the ganglionic cells and the terminal 
vesicles ; So, nerve terminations of the organ of Siebold ; vT, 
front tympanum ; vTr, front branch of the trachea . . .,. 103 

66. Auditory rod of a grasshopper (Gryllus viridissimus). fd', 

Auditory rod ; ko, terminal piece . . . . . , 194 

67. Diagram of a section through the auditory organ of a grass- 



xvi LIST OF ILLUSTRATIONS. 

FIGURE PAGE 

hopper (Meconema). c, Cuticle ; a.r, auditory rod ; a.c, 
auditory cell ; tr, trachea . . . . . . . . . . 105 

68. Outer part of a section through the tibia of a Gryllus viri- 

dissimus. h, Hard surface of leg ; tr, trachea ; F, fat bodies ; 
Su, suspensor of the trachea ; v W, tracheal wall ; TN, nerve ; 
gz, ganglionic cells ; rb, tissue connecting the ganglionic cells ; 
E. 8ch., end tubes of the ganglionic cells, each containing an 
auditory rod ; fa, terminal threads of ditto . . . . . . 106 

69. Tibia of yellow ant (Lasius flavus), X 75. 8, 8, Swellings of 

large trachea ; rt, small branch of trachea ; a, auditory organ 107 

70. Part of the tibia of Isopteryx apicalis. 8c, Auditory organ ; 

ef, terminal filament ; Cu, cuticle ; G, ganglionic cell ; So, 
structure enclosing the auditory rod ; tr, trachea ; n, nerve 109 

71. One of the halteres of a fly .. .. .. .. .. 110 

72. Right half of eighth segment of the body of the larva of a gnat 

(JJorethra plumicornis). EG, Ganglia; N, nerve; g, auditory 
ganglion ; gb, auditory ligament ; Ch, auditory rods ; a, audi- 
tory nerve ; e, attachment of auditory ligament to the skin ; 
Tin, hn', termination of skin-nerve ; tb, plumose tactile hair ; 
h, simple hair ; tg, ganglion of tactile hair ; Im, longitudinal 
muscle .. .. .. .. .. .. .. ..114 

73. Head of a gnat .. .. .. .. .. .. .. 115 

74. Diagram showing one possible mode of vision . . . . . . 119 

75. Diagram showing a second possible mode of vision .. .. 119 

76. Diagram showing a third possible mode of vision . . . . 120 

77. Diagram of human eye. G, Vitreous humor ; L, lens ; W, 

aqueous humor ; c, ciliary process ; d, optic nerve ; e e, sus- 
pensory ligament ; k k, hyaloid membrane ; f f, h h, cornea ; 
g, choroid ; *, retina ; I, ciliary muscle ; mf, nf, sclerotic coat ; 
p p, iris ; s, the yellow spot. . . . . . . . . 121 

78. Section through the retina. 1, Limitary membrane ; 2, layer 

of nerve-fibres; 3, layer of nerve-cells; 4, nuclear layer; 5, 
inner nuclear layer ; 6, intermediate nuclear layer ; 7, outer 
nuclear layer ; 8, posterior membrane ; 9, layer of small rods 
and cones ; 10, choroid . . . . . . . . . . . . 123 

79. A, Inner segments of rods (5, s, s) and cones (z, z') from man, 

the latter in connection with the cone-granules and fibres as 
far as the external molecular layer, 6. In the interior of 
the inner segment of both rod and cone fibrillar structure is 
visible. X 800 124 

80. Diagram to prove the existence of the blind spot in the eye . . 125 

81. Pineal eye-scale on the head of a small lizard (Calotis) . . 127 



LIST OF ILLUSTKATIONS. XVll 

FIGURE PAGE 

82. Diagram of a section through the skull and pineal eye of Lacerta 

viridis. C, Cuticle ; Pa, parietal bone ; Ep, epidermis ; L, 
lens ; Pig, Pigment ; R, rete mucosum ; CH, cerebral hemi- 
sphere ; N, nerve ; Ep, epiphysis ; OpL, optic lobe of brain 128 

83. Englena viridis. e, Eye-spot . . . . . . . . 130 

84. Section through the simple eye of a young Dytiscus larva. /, 

Corneal lens ; g, cells forming the vitreous humor ; r, retina; 

0, optic nerve ; h, hypoderm . . . . . . . . . . 131 

85. Eye-spot of Lizzia. oc, Ocellus ; /, lens . . . . . . 132 

86. Eye-bulb of Astropecten 132 

87. Eye of Asteracanthion. c, Cuticle ; e, epithelium ; I, lens ; p, 

pigment . . . . . . . . . . . . . . . . 133 

88. Anterior extremity of a freshwater worm (Bohemilla comata). 

a, Eye; b, brain; c, cuticle; hp, hypoderm; lb, tactile hair; 

ne, nerve ; v, blood-vessel . . . . . . . . . . 135 

89. Eye-dot of Nereis. In B the pigment is partly removed so as 

to show the lens . . . . . . . . . . . . 135 

90. The first twelve segments of Potyophthalmus pictus, seen from 

below. The Roman numerals indicate the segments. St, 
Papillae on the head ; KS, head ; au, head eye ; s.au, side eyes ; 

01, upper lip ; 07, under lip ; v.ph, pharyngeal vein ; V.subinta, 
anterior ventral vein ; V.d.l 1 -*, veins connecting the superior 
lateral and vessels ; sept 1 - 3 , intersegmental^ membranes ; 
m.ocs.l, lateral muscle of the oesophagus ; V.ann, pulsating 
circular vessel ; Md.dr, stomach-glands ; V.v-l, vein con- 
necting the inferior and lateral blood-vessels ; Md, stomach ; 
Bm, muscles of the hairs ; G, brain ; fl.o, ciliated organ ; am, 
transverse muscle .. .. .. .. .. ..136 

91. Alciope 137 

92. Perpendicular section through the eye-pit of a limpet (Patella). 

1, Epithelial cells ; 2, retina cells ; 3, vitreous body . . 138 

93. Eye of Trochus magus. Gl, Vitreous body ; No, nerve . . 138 

94. Eye of Murex brandaris. L, Lens; Gl, vitreous body ; No, nerve 139 

95. Eye of Helix pomatia. ct, Cuticle ; a, epithelium ; b, cornea ; 

c, envelope of the eye ; d, cellular layer ; e, fibrils of the optic 
nerve ; /, feeler cell ; na, nerve of the tentacle ; no, optic 
nerve . . . . . . . . . . . . . . . . 140 

96. Perpendicular section through an eye of Area noce. 1, Epithe- 

lium of the edge of the mantle ; 2, cells of vision ; 3, lens ; 

4, 5, connective tissue ; 6, section of one of the cells . . 142 

97. Diagram of eye of Pecten. a, Cornea ; 6, transparent basement 

membrane supporting the epithelial cells of cornea; c, the 



XV111 LIST OF ILLUSTRATIONS. 

FIGURE PAGE 

pigmented epithelium; d, the lining epithelium of the mantle ; 
e, the lens ; /, the ligament supporting the lens ; g, the 
retina ; A, the tapetum ; k, the pigment ; m, the retinal 
nerve ; n, complementary nerve . . . . . . . . 143 

98. Schematic representation of the soft and some of the hard parts 

in a shell of a Chiton (Acanthopleura), as seen in a section 
vertical to the surface, and with the margin of the shell lying 
in the direction of the left side of the drawing, a, Conical 
termination of sense-organ ; b, b', ends of nerve ; c, nerve ; /, 
calcareous cornea ; g, lens ; h, iris ; k, pigmented capsule of 
eye ; m, body of sense-organ cut across ; n, nerve of eye ; p, 
nerve of sense-organ ; r, rods of retina . . . . . . 145 

99. Long section through the front (J.) and hinder (i?) dorsal eyes 

of Epeira diadema. A, Anterior eye ; B, posterior eye ; Up, 
hypoderm ; Ct, cuticle ; ct, boundary membrane ; M, muscular 
fibres; M, M 1 , cross sections of ditto; St, rods; Pg, P l , pig- 
ment cells ; L, lens ; Gk l , vitreous body ; K, nuclei of the cells 
of the retina ; Kt, crystalline cones ; Et, retina ; Nop, optic nerve 147 

100. Section through the eye of a cockchafer (Melolontha). . . . 148 

101. Section through the eye of a fly. b.m, Basilar membrane ; c, 

cuticle ; e.op, epioptic ganglion ; n.c, nuclei ; n.c.s., ner^e-cell 
sheath ; N.f, decussating nerve-fibres ; op, optic ganglion ; pc, 
pseudocone; pg, pigment cells; p.op, perioptic ganglion; r, re- 
tinula; Eh, rhabdom; T, trachea; t.a, terminal anastomosis ; 
Tt, trachea ; ti, tracheal vesicle . . . . . . . . 149 

102. Two separate elements of the faceted eye of a bee. Lf, Cornea ; 

n, nucleus of Semper ; Kk, crystalline cone ; Pg, Pg 1 , pigment 
cells; PI, retinula ; Em, rhabdom .♦ .. .. ..150 

103. Eyelet of cockroach. If, Cornea ; kk, crystalline cone ; pg', pig- 

ment cell ; rl, retinula ; rm, rhabdom . . . . . . 152 

104. Eyelet of cockchafer. If, Cornea ; kk, crystalline cone ; pg,pg\ 

pigment cells ; rl, retinula; rm, rhabdom .. .. .. 152 

105. Leptodora hyalina . . . . . . . . . . . . 156 

106. Eye of Mysia. n, Nuclei ; Lf, facets ; Kk, crystalline cones ; 

W 1 , cells of the retinula ; El, retinula ; Em, rhabdom ; Cp, 
blood-vessels ; N, fibres of the optic nerve ; JV 11 , N U1 , N uu , 
decussations of the fibres of the optic nerve ; G, G 1 , ganglia ; 
M, muscles for the movement of the eye-stalk ; Km, nuclei . . 157 

107. Cory casus, a, 6, The eye . . . . . . . . . 158 

108. Eyes of Calanella Mediterranea. Pg, pigment cells ; Nfr, 

frontal nerves ; N.op, nervus opticus. The numbers show 

the numbers of the cells . . . . . . . . . . 159 



LIST OF ILLUSTEATIONS. XIX 

FIGURE PAGE 

109. Diagram of a vertical section through a portion of the lateral 

eye of Limulus polyphemus, showing some of the conical lenses, 
and corresponding retinulse. a, Cuticle; 66, cuticular lens; 
cc f hypoderm; En, retinula; n, nerves .. .. .. 160 

110. Euphausia pellucida. l.o 9 Luminous organ .. .. .. 161 

111. Luminous organ of Euphausia. /, Fibres ; e, lens .. .. 162 

112. Eye-stalk of Euphausia. lo, Luminous organ; a, lower eye . . 162 

113. One of the elements of the eye of a fly. kk, Crystalline cone ; 

x, position of the image; s, rod; sc, sheath; scm, outer 
sheath; r, retina ; y, seat of vision .. .. .. .. 166 

114. Photichthys argenteus .. .. .. .. .. .. 185 

115. Ceratius bispinosus . . . . . . . . . . 186 

116. Edge of a portion of the mantle of Aglaura hemistoma, with a 

pair of sense-organs, v, Velum ; k, sense-organ ; ro, layer of 
nettle cells ; t, tentacle . . . . . . . . . . 188 

117. Sense-organ of leech. 1, Epithelium ; 2, pigment ; 3, cells ; 

4, nerve . . . . . . . . . . . . . . . . 189 

118. Daphnia pulex. «, Antennas ; 6, brain ; e, eye ; h, heart ; m, 

muscle of eye ; w, nerve of eye ; o, ovary ; ol, olfactory organ ; 

5, stomach ; y, three eggs deposited in the space between the 
back and the shell . » , , . . , . « , . . 211 



LIST OE THE PEIFCIPAL MEMOIES, ETC., 
EEEEEEED TO IN THE PBESENT WOEK. 



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Anz., 1886. 
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Becher, Zur Kenntniss der Mundtheile der Dipteren, Benkschr. der Acad. 

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Bela Haller, Untersuchungen iiber marine Rhipidoglossen, Morphol. 

Jahrb., 1884. 
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1887. 
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Zeit. fur Biologie, 1884. 
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2 



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Briant, T. T., On the Anatomy and Functions of the Tongue of the Bee, 

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Carriere, J., Die Sehorgane der Thiere. 1885. 

Claparede, E., Morphologie des zusammengesetzten Auges bei den Arthro- 

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, Anat. and Ent. d. Retina, Mailer's Archiv, 1857. 

, Sur les pretendus organes auditifs des Antennes chez les Cole- 

opteres, Ann. Sci. Nat., 1858. 
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Zool, 1863. 
Comparetti, Dinamica animale degli insetti. Padoue : 1800. 

, De aure interna comparata-Patavii. 1789. 

Cornalia, Monografia del Bombice del Gelso, Mem. d. R. istit. Lombardo di 

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Dahl, Das Gehor-und Geruchsorgan der Spinnen, Arch, fur Mik. Anat., 

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1861. 
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Eimer, Dr. Th., Ueber Tast-apparate bei Eucharis multicornis, Arch, 
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Erichson, De fabrica et usu antennarum in insectis. Berlin: 1847. 

Exner, S., Ueber das Sehen von Bewegungen und die Theorie des zusam- 
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, Die Frage der Functionsweise der Facettenangen, Biol. Centralblatt, 

1881, 1882. 



MEMOIRS, ETC., REFERRED TO. xxiii 

Fabre, J. H., Souvenirs Entomologiques. Etudes et Flnstinct sur les Moeurs 
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, Nouveaux Souvenirs Entomologiques. 1882. 

, Souvenir Entomologiques, troisieme serie. 1886. 

Farre, On the Organ of Hearing in Crustacea, Phil. Trans., 1843. 
Forel, A., Les fourmis de la Suisse, Geneve. 

, Experiences et Remarques Critiques sur les Sensations des Insectes, 

Recueil Zool. Suisse, 1887. 
Fraisse, Ueber Molluskenaugen, Zeit. fiir Wiss. Zool., 1881. 

Gazagnaire, J., Orig. de la gust, chez les coleopteres, Proc. verb, de la Soc. 

Zool. de France, 1886. 
Gegenbaur, Beit, zur Kennt. der Gastropodenaugen, Gegenbaur's Morph. 

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Goldschneider, Dr. A., Monath. fiir prackt. Dermatologie, 1884. 

, Die spezif. Energie der Temperaturnerven. 

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Gottsche, C. M., Beitrag zur Anatomie und Physiol, des Auges der Fliegen 

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— — , Ueber das unicorneale Tracheaten-und speciell das Arachnoiden-und 

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— — , Morphologische Untersuchungen iiber die Augen der freilebenden 

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Nat. Hist., 3rd ser., 1859. 



MEMOIRS, ETC., REFERRED TO. XXV 

Hickson, S. J., The Eye of Pecten, Quar. Jour. Mic. Soc, 1880. 

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Houzeau, J. C, Etudes sur les Facultes Mentales des Animaux. 

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Wiss. Zool., 1883. 
, Ueber die Geruchsorgane der Gliederthiere, Osterprogr. d. Realschule 

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Krohn, A., Ueber augenahnliche Organe bei Pecten und Spondylus, Arch. 

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, Zool. und Anat. Bemerk. iiber die Alciopiden, Wiegmann's Arch., 

1845. 
Kiinkel et Gazagnaire, Du siege de la gustation chez les Insectes dipteres, 

Comptes rendus des Sci. Nat., 1881. 
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Landois, Das Gehororgan des Hirschkafers, Arch, fiir Mic. Anat, 1868. 
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vol. xvii. 

, Thierstimmen. 

Lange, W., Beit, zur Anat. und Hist, der Asterien und Ophiuren, Morph, 

Jahrbuch, 1876. 



XXVI MEMOIKS, ETC., EEFEKRED TO. 

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Lankester, E. Ray, Observations on the development of the Cephalopoda, 

Quar. Jour. Mic. Soc, 1875. 
— - and Bourne, A. G., The Minute Structure of the Lateral and the 

Central Eyes of Scorpio and of Limulus, Quar. Jour. Mic. Soc, 1883. 
Lebert, Hermann, Die Spinnen der Schweiz. 

Lee, Bolles, Les Balanciers des Dipteres, Becueil Zool. Suisse, 1885. 
Leeuwenhoek, Select Works, Translated by H. Hoole. 
Lehmann, De sensibus externis animalium exsanguium, insectorum scilic, 

ac vermium, commentatio. Goettingae : 1798. 
, De Antennis Insectorum Dissertatio prior, fabricam antennarum 

describens. Hamburgi : 1799. 
, De Antennis Insectorum Dissertatio posterior, usum antennarum 

recensens. Hamburgi : 1800. 
Leroy, C. G., Intelligence and Perfectibility of Animals. 
Lespes, Mem. sur l'appareil auditif des Insectes, Ann. Sci. Nat., 1858. 
Leuckart, R., Ueber muthmassliche Nebenaugen bei einem Fische, 39 Bericht 

Deutscher Naturforscher. Giessen : 1864. 

, Carcinologisches, Wiegmann's Arch., 1859. 

, Organologie des Auges, in Graefe und Saemisch, Handbuch der 

gesammten Augenheilkunde, 1874. 
Leydig, F., Carcinologisches, Wiegmann's Arch, 1858. 
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1859. 
, Ueber Geruchs und Gehorogane der Krebse und Insekten, Muller's 

Arch., 1860. 

, Die Augen und neue Sinnesorgane der Egel, Beicher^s Arch., 1861. 

, Das Auge der Gliederthiere. 1864. 

, Die Augenahnlichen Organe der Fische. 1881. Tint. z. Anat. und 

Hist, der Thiere. 1883. 

, Die Hautsinnesorgane der Arthropoden, Zool. Anz., 1886. 

Locy, W. A., Obs. in the Dev. of Agelena, Bull. Mic. Comp. Zool. 

Harvard: 1886. 
Lowne, B. Thompson, On the Simple and Compound Eyes of Insects, Phil. 

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, On the Compound Vision and the Morphol. of the Eye in Insects, 

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, On the Anatomy of Ants, Microscopical Journal, 1877. 

, On the Anatomy of Ants, Trans. Linn. Soc, 1880. 

, Ants, Bees, and Wasps. 1886. 

, On the Sense of Color among some of the Lower Animals, Jour. 

Linn. Soc, 1881. 



MEMOIRS, ETC., REFERRED TO. XXV11 

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1879. 
Mayer, Dr. P., Sopra certi Organi di Senso nelle Antenne dei Ditteri, 

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Meinert, Bid. til. de Danske Myrers Xatur. Hist. 1860. 

, Die Mundtheile der Dipteren, Zool. Anz., 1882. 

Merejkowsky, M. C, Les Crustaces inferieurs distinguent-ils les couleurs ? 
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Mic. Anat., 1882. 
Moseley, On the Presence of Eyes in Shells of certain Chitonidse, Quarterly 

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xxviii MEMOIRS, ETC., REFERRED TO. 

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deutsch. Akad. d. Naturf., 1875. 



ON THE 

SENSES, INSTINCTS, AND INTELLIGENCE 

OP 

ANIMALS. 

CHAPTER I. 

INTRODUCTORY REMARKS. 

The organs of sense may be said to be the windows 
through which we look out into the world, and it has 
always been to my mind one of the most interesting 
problems of natural history, to consider in w T hat manner 
external objects affect other animals, how far their 
perceptions resemble ours, whether they have sensations 
which we do not possess, and how we ourselves arrive 
at our own perceptions. 

I propose to dwell in the present work especially on 
the senses of insects, partly because my own observa- 
tions have been made principally on them, and partly 
because their senses have, perhaps, been on the whole 
more thoroughly and successfully studied than those 
of the other lower animals ; which again arises from 
the fact that no group offers more favourable oppor- 
tunities for the study of these organs. The subject is 
no less vast than difficult, and I do not pretend in any 
way to give a complete view of the whole question, 



2 DIFFICULTY OF THE SUBJECT. 

but have selected those cases which seemed to me the 
most suggestive, interesting, and instructive. 

No one can doubt that the sensations of other animals 
differ in many ways from ours. Their organs are some- 
times constructed on different principles, and situated 
in very unexpected places. There are animals which 
have eyes on their backs, ears in their legs, and sing- 
through their sides. Nevertheless, in considering the 
different senses, it will probably be most convenient to 
begin by a short summary of our own organs, as afford- 
ing the best clue to the purposes and functions of cor- 
responding structures among the lower animals. The 
subject is one of very great difficulty. Even as regards 
our own senses, we are still in extreme ignorance. The 
clue afforded by anatomy is very imperfect, and some- 
times almost misleading. No one can read the literature 
relating to the organs of sense without feeling how 
very little we really know on the subject. Even when, 
as especially in the cases of the organs of hearing and 
sight, we have careful and elaborate descriptions and 
figures of very complex structures, these relate rather 
to the separation and arrangement of the waves of sound 
or light, than to the actual manner in which they affect 
the nervous system itself ; while as to the manner in 
which our perceptions are in turn created, we are almost 
absolutely ignorant. In the senses of taste and smell 
this becomes, perhaps, even more clearly evident. 

Every cell, indeed, in the animal body is a standing 
miracle. Consider what it has to do. It must grow ; it 
must assimilate nourishment ; it must secrete ; it must 
produce other cells like itself; and this often in addition 
to its own proper and distinctive function. The lowest 
animals consist but of a single cell. Yet they feed and 



THE LIFE OF A CELL 3 

digest ; they grow and multiply ; they move and feel. 
Their perceptions, indeed, are no doubt confused and 
undifferentiated, and perhaps devoid of consciousness. 
The soft protoplasm of which they consist is dimly 
affected by external stimuli, as, for instance, by the 
waves of light or of sound. These forms, however, are all 
minute, and, indeed, almost invisible to the naked eye. 
The larger animals are built up of a number of cells. 

Let us, then, consider the possible modes in which an 
organ of sense, say an eye, may have originated. 

In the simpler forms, the whole surface is more or less 
sensitive. Suppose, however, some solid and opaque 
particles of pigment deposited in certain cells of the skin 



HOI 



Fig. 1. — Diagram of skin, c, Cuticle ; h, cellular or hypodermic layer. 

(Fig. 1). Their opacity would arrest and absorb the 
light, thus increasing its effect, while their solidity would 
enhance the effect of the external stimulus. A further 




Fig. 2. — Diagram of skin, c, Cuticle ; h, cellular or hypodermic layer. 

step might be a depression in the skin at this point, 
which would serve somewhat to protect these differen- 
tiated and more sensitive cells, while the deeper this 
depression the greater would be the protection. 

The epithelial cells frequently secrete more or less 
matter, which may form a more or less solid ball. 
This might be set in vibration by the sound-waves, 
and would thus increase the effect on the epithelial 



4 POSSIBLE MODES OF ORIGIN. 

cells. Such a body is known as an otolithe. On the 
other hand, it might serve as a lens, and by condensing 




Fig. 3.— Diagram of origin of a sense-organ, c, Cuticle ; h, hypoderm ; * n, nerve. 

the light would act like a burning-glass, and increase 
its effect on the cells below. A farther stage would be 



c 

h 




Fig. 4 Diagram of further stage in the origin of a sense-organ. 

that the immediately subjacent cells, acted on by the 
increased stimulus, might (Figs. 3 and 4) develop into 
special nerve-tissue. 

* I.e. the cellular layer below the cuticle. 



OF SENSE-ORGANS. 5 

Nor is this a merely imaginary case. Each of the above 
stages may be found in actual existence— that, for in- 
stance, indicated in Fig. 2 in the limpet (Fig. 92) ; Fig. 3, 
in Trochus (Fig. 93) ; and Fig. 4 in the snail, Helix 
or Murex (Figs. 94, 95). Eecent researches indicate 
that the eyes of Artieulata (insects, etc.) have, in some 
cases at least, a similar history. But more than this, 
if the development of the eye of an individual snail be 
watched in the egg, it will be found to pass successively 
through stages resembling Fig. 2, then Fig. 3, and 
then Fig. 4. 

In other cases, however, the organs of sense have a 
different origin and history. Suppose, for instance, 



c 



Fig. 5.— Diagram of origin of a sense-organ. 

that the hypodermic layer were at any spot (Fig. 5) 
somewhat more strongly developed than elsewhere ; in 
that case, the cuticle secreted by the hypodermic cells 
would tend to be rather thicker than usual. This would 
again (Fig. 6) constitute a lens, and serve to condense 
the light. That certain eyes have actually arisen in 
this way is indicated by Fig. 7, representing a section 



*m 



Fig. 6. — Diagram of further stage in the origin of a sense-organ. 

through the eye of the larva of a water- beetle 
(Dytiscus). Nor, as we shall presently see, do these 
two types of development by any means exhaust the 
ways in which eyes may originate. In the two cases 
given the eyes originate from the skin, but in others — 
for instance, in ourselves — the percipient elements are 
formed from the central nervous system. 



6 



ORIGIN OF EYE AND EAR. 




The tissues of the lowest animals have not been shown 
to contain any special nerve-fibres, but underneath those 

parts of the surface 
where, either in the 
roannerindicated above, 
or in some other, the 
effects of external stim- 
uli are heightened by 
any structural modifi- 
cations, there would be 
a tendency to the speci- 

Fig. 1.— Section through the simple eye of a a li Z Q+i on f an pvoeil- 

young Dytiscus larva (after Grenadier), h, dl,Zdlluu VL dU «*^P 

Hypoderm; Z lens ; o optic nerve; g, p, tionally Sensitive tisSU6. 

modined hypodermic cells ; r, retma. J 

Moreover, such an 
organ as that represented in Fig. 4 might serve either 
as a rudimentary ear or an eye. It might, indeed, be 
acted on by the waves both of light and of sound. Such 
organs — as, for instance, in the case of marginal bodies 
round the edge of certain jelly-fishes (Medusae; see 
Figs. 8 and 50) — have been regarded by some naturalists 

as eyes, and by others as 
ears. Haeckel suggests * that 
some may be warmth-organs. 

Fig. 8 represents one of the 
marginal sense-organs of a 
Medusa (Ontoehis), where we 
have a row of brilliantly re- 
fractive spherules, which from 
analogy are considered to serve 
as otoliths ; but which, under other circumstances, 
might be, and in fact have been by some, regarded 
as the lenses of a simply constructed organ of vision. 

* " Keport on Deep Sea Medusae," " Challenger Keports," vol. iv. 




Fig. 8. — Auditory vesicle of Onto- 
ehis (after Haeckel). 



THE SENSE OF TOUCH. 7 

Even among the most highly specialized organs of 
sense, it is impossible not to be struck by the similarity 
between the cones in the retina (Fig. 79) and certain 
organs in the antennae of insects (Fig. 42) which are 
generally considered as olfactory. It does not follow 
that an organ with a nerve, a lenticular body, and 
pigment, should necessarily be an eye. Nor, on 
the other hand, is there anything in the structure 
of the organs, for instance, of smell or taste which 
throws any light on the perceptions we receive from 
them. That there should be separate nerve-fibrils in 
our own skin, not only for the sensations of temperature 
and of touch, but, as appears from the researches of 
Blix and G-oldschneider, even of heat and of cold, we 
had not anticipated a priori; and it would be difficult 
to prove in any animal but ourselves. 

The Sense of Touch. 

I commence with the sense of touch, as being the 
one which is most generally distributed, and from 
which the others appear to have been in some cases 
developed. The senses are not, indeed, as already 
mentioned, always to be easily distinguished from one 
another; and it would seem that the same nerve may 
be capable of carrying different sensations according to 
the structure of the end organs. 

The sensibility of our skin appears to be mainly due 
to a plexus of fine nerve-fibres, which end in free termi- 
nations between the cells of the skin (rete mucosum). 
There are also in some parts of the skin two sets of 
minute corpuscles, which are called after their discoverers, 
the first Vaterian, or more commonly Pacinian, cor- 
puscles; the second, Meissner's or Wagner's corpuscles. 



8 



THE ORGANS OF TOUCH. 



The Pacinian corpuscles consist of a capsule formed 
of several layers, one enveloping the other. The 
undulating nerve-fibres, after several windings, enter 
the capsule, which, indeed, seems to be nothing 
more than a much-thickened end of the outer nerve- 
coat. These corpuscles measure from 11 to 4'5mni. 
They occur principally on the hands and feet, and 
in the flexures of the joints, but occasionally also 
elsewhere. 





Fig. 9.— Pacinian corpuscle (after Leydig). 
a, Neurilemma ; b, nerve-fibril ; c, cap- 
sule ; d, peculiar fibres ; e, central 
cylinder. 



Fig. 10. — Papilla from the surface of 
the hand, x 350 (alter Kolliker). a, 
Cone-like body ; b, nerve ; c, end of 
nerve. 



Meissners or Wagner's corpuscles are cone-like or 
egg-shaped bodies, in each of which a nerve termi- 
nates, after several convolutions. They are especially 
numerous at the tips of the fingers, where there may 
be as many as a hundred in a square line. They 
occupy the papillae (which, however, do not always 
contain one), which give the surface of the hand its 
peculiar striped appearance. They also occur, though 
less numerously, elsewhere, as on the feet, breast, and 
lips. 



NEKVES OF TOUC&. 9 

It appears probable, however, that these are not 
really the organs of touch, but rather, perhaps, guards 
or protectors of the true and very sensitive organs 
within. They are, no doubt, most numerous on the 
more sensitive parts of the skin, such as the hands and 
tongue, and the sense of touch is most acute where they 
occur; but they appear to be absent in some places 
where the sense of touch certainly exists, and they 
are abundant again in the foot, which, though not 
especially sensitive, is particularly exposed. 

The sensation of pressure is intimately associated 
with the hairs, which no doubt serve, at any rate in 
some cases, for protection, but which, in Blix's * opinion 
are in man probably all organs of touch. 

We have still indeed much to learn as to the 
terminations of the nerves in the skin. It would seem 
that some are connected with cells, while others termi- 
nate in a free point. Merkel has suggested that those 
which end in cells are the true nerves of touch, while 
the free nerves record changes of temperature. Others, 
perhaps w 7 ith more probability, have supposed that the 
free nerves convey merely a general and undifferen- 
tiated sensation, while those which terminate in cells 
give the specific impressions of pressure, heat, cold, 
etc., any one of which may be intensified into pain. 

However, this may be, Blix * and, shortly afterwards, 
Goldschneider f have made the interesting discovery 
that we do not feel changes of pressure and of 

* " Exper. Beitr. zur Losung der Frage iiber die Specif. Energie der 
Hautnerven," Zeit. filr Biologie, 1 885. Blix's previous papers in Upsala 
Lakan-forenings Forhandlingar, 1882, I have not seen. 

f "Monatschr. fur prakt. Dermatologies 1884. " Neue Thatsachen 
ii. die Hauptsinnesnerveii," Zool. Anz., 1885 und 1886. 



10 



SENSE OF TEMPERATURE. 



temperature at the same points of the skin or by the 
same nerve-ends. The feeling of pressure seems to 
be intimately associated with the hairs, which is not 
the case with sensations of temperature. Even the 
feelings of heat and cold are also separate. These 
three sets of points, indeed, are so near together that 
the separation had hitherto not been observed, espe- 
cially as they are closely intermixed. They have a 
tendency, however, to arrange themselves in more or 
less curved lines. Goldschneider experimented with 
a fine point, which he passed over the skin, thus 
testing it sometimes for pressure, sometimes with 
a warm point for heat, sometimes with a cold point for 



CJP 




Fairs 




;'v "'.''* 




• • ■ • • 






V* 


• ♦ • * 

• • • •« 


y* 



WP 




Fig. 11.— Portion of the skin of the back of the hand (after Goldschneider). The 
centre figure represents the arrangement of the hairs; CP, the cold-points ; WP. 
the warmth-points. 

cold. Moreover, if he raised the points thus determined 
with a fine needle, and snipped off the fragment of the 
skin, he found that the resulting sensation was quite 
different in the three cases. If the point removed 
was a " pressure-point " the sensation was one for the 
moment of pain; while the temperature-points gave 
one respectively of heat or cold. The terminations of 
the temperature-nerves are, according to Goldschneider, 
much finer than those of the pressure-nerves, and they 
are also fewer in number. He cut out from his own 
skin a large number of sensitive points, but, w r hile he 
found that each corresponded to a nerve-end, he has 
not been able to discover any difference at or in the 



ORGANS OF TOUCH AMONG LOWER ANIMALS. 11 

termination of the nerves corresponding to these differ- 
ent sensations, though it may reasonably be expected 
that such must exist. 

The question has arisen whether there are separate 
nerve-endings for pain, as apart from pressure, etc. ; but 
the observations of Blix and Goldsclmeider appear to 
show that pain arises merely from the intensification of 
other impressions, and that it does not reside in any 
special organs. 

Sense of Touch among the Lower Animals. 

Among the lower animals the outer skin is often 
very sensitive, but we know scarcely anything as to the 
minute structure of the organs of tactile perception. 
In some cases they are, no doubt, very simple ; but in 
others it will probably be found that the apparent 
simplicity is due to our deficient information and means 
of investigation, rather than to any want of complexity 
ia the organs themselves. 

In the Coelenterata (zoophytes, etc.) certain setae, 
especially on the tentacles and near the mouth, are 
generally regarded as organs of touch. 

In the epithelium of many of the lower animals, two 
forms of cells may be detected. Some unmodified, or 
indifferent, which form the general substance of the 
epithelial layer ; others more or less specialized, which 
are seldom absolutely contiguous, but generally sepa- 
rated by one or more of the indifferent cells. 

In other cases, nerves may end abruptly at the 
cuticle without the latter presenting, so far as our 
present means of investigation have shown, any ap- 
parent change ; as, for instance, in the following 



12 



MEDUSA. 



figure of a part of the skin of 
(Nereis). 

\8 \8a 



small 



worm 




Fig. 12. — Half of a cross section through the brain and hinder pair of eyes of Nereis 
■cultrifera (after Carriere). 1, Hypoderm ; 2, cuticle ; 3, retina ; 4, outer corneal 
cells; 5, inner corneal cells; 6, brain ; 8, $a, two places to which the brain sends 
large nerves (9), but where the cuticle is unaltered ; g, gelatinous body. 

Among the Medusae (jelly-fishes), also, the supposed 
tactile organs are ciliated cells (Fig. 13), which scarcely 
differ from the other epithelial cells, but which ter- 
minate externally in a cilia, and internally in a nerye- 
fibril. 




Fig. 13.— Part of upper nerve-ring and tactile epithelium of Lizzia (after Hertwig). 
a, Tactile epithelium; g, ganglionic cell; nr 1 , upper nerve-ring. 

In other cases, the tactile hairs scarcely differ from 
those covering the general surface. Fig. 14 represents 
part of the skin of a sea-anemone, the long cylinders 
are nematocysts, or thread-cells — elastic sacs, in the 



ANNELIDES. 



13 



interior of which lies coiled up a long filament, which 

is often serrated at the end. Even a 

very slight pressure causes this thread 

to spring out, and these little darts, 

which are present in immense numbers 

in the skin of Hydrozoa (jelly-fish, etc.), 

serve both as weapons of defence and 

also to wound the small animals on 

which they feed. 

nz represents a nerve-cell, and it will 
be seen that the hair in w 7 hich it ter- 
minates does not materially differ from 
the rest. 

In the Annelides, also, the general 
surface of the integument (Fig. 15) 
presents tactile setae or cilise, which are scattered over 




Fig. 14. — Diagram of 
part of the skin of 
a sea-anemone (Ac- 
tinia); after Korot- 
neff. clz, Glandular 
cell ; nz, nervous 
cell. 




Fig. 15. — Anterior part of body of Bohemilla comata (after Vejdovsky *). 76, Tactile 
hair ; hp, hypoderm ; c, cuticle ; b, anterior part of brain ; a, eye ; ne, nerve- 

fibrhs ; v, anterior blood-vessel. 

the surface, and especially on the head. In some cases 
* " Syst. and Morph. der Oligochceten." 1884. 



14 



MOLLUSCA. 



these setae are collected into special groups, either 
situated in cup- shaped depressions of the skin, or on 
more or less elevated papillae. Fig. 15 represents the 
anterior part of the body of a small fresh-water worm 
(Bohemilla), and shows clearly the small cuticular, and 
the larger tactile, hairs. In other cases, as in the feelers 
and cirri of the Alciopidae, there are short, shining, 
ovoid rods, to the base of which runs a nervous fibril. 

In the Mollusca, also, the surface of the skin is very 
sensitive, and is generally provided with minute setae, 
especially on the tentacles, or as in Lameliibranchiata 
(mussels, etc.), on the edge of the mantle. In some, the 
snail for instance (Helix), the nerves, on approaching 
the skin, have been ascertained to divide into a plexus 
of fibrils. 




Fig. 16. — Diagrammatic section through a papilla of touch of Onchidium (after Semper). 
a', a", Two layers of the cuticle; a, biconvex thickened portion of the cuticle; 
b, enlarged epithelial cells ; b', ordinary epithelial cells ; c, cellular body ; d, cells ; 



n, nerve. 



In Onchidium, a genus of slugs, Semper describes as 
organs of touch (Fig. 16) certain slight elevations of the 



MOLLUSCA. 



15 



skin caused by the cuticle being somewhat thickened. 
Beneath these the epithelial cells are larger than usual; 
and under them, again, lies a cellular mass, the minute 
structure of which he was not able to determine, but 
which is connected with a nerve. 

On the mantle of the Chitons are also certain 
well-defined organs, probably of touch. They occupy 
pores in the shells, and resemble obconical or somewhat 
dice-box shaped plugs of transparent, highly refracting 




Fig. 17. — Diagram of the structure of the soft and some of the hard parfs in the teg- 
mentum of a shell of a Chiton (Acanthopleura spiniger), as seen in a section vertical 
to the surface and with, the margin of the shell bordering on the girdle lying in the 
direction of the left side of the drawing, f, Calcareous cornea ; h, iris ; g, lens ; 
Jc, pigmented capsule of eye ; n, optic nerve ; r, rods of retina ; n', branches of 
the optic nerve, perforating the capsule wall, and terminating in b', b', b', ocular 
sense-organs ; p, p, nerves to sense-organ ; m, body of sense-organ cut across ; 
a, p, fusiform body of sense-organ entire ; a, obconical termination of sense- 
organ; e, nerve given off by one sense-organ to another, b". 

tissue. The terminal knobs end in flat discs, which 
show a series of concentric rings, as if composed of a 
series of concentric layers or inverted cones fitted one 
within the other.* Each one terminates in a nerve- 



Moseley, Quarterly Journal of Microscopical Society, 1885. 
3 



16 



CRUSTACEA AND INSECTS. 



fibre. They are of two distinct sizes, which Moseley 
proposes to call macroesthetes and microesthetes. 

In many animals, as in ourselves, the outer skin is 
soft and susceptible to external impressions. In Insects 
and Crustacea on the contrary, the inner skin, or hypo- 
derm, is covered with a more or less thick layer of 
horny substance known as chitine ; and, from the 
nature of their chitinous integument, it naturally 
follows that the sensations of insects, excepting that 
of sight, are effected by means of variously modified 
hairs. We know, however, so little, in the first place, 
as to the real means by which animals, including 
man, hear, smell, or taste, and, in the second, as to the 
intimate structure of their minute organs, that we are 
often in doubt, and there are still great differences of 
opinion whether a given sense-hair serves for hearing, 
smell, or touch. 
The hairs of Arthropods belong to very different 



1/ 




mm 



Fig. 18. — Diagram of forms of hairs in insects, a, Ordinary surface hair ; 5, plumose 
natatory hair ; c, hair of touch ; d, auditory hair ; e, olfactory hair ; /, taste hair ; 
n, nerve hair. 

categories, some of which we may perhaps distinguish 
as follows : — 

Those under which the chitinous integument is entire. 

1. Ordinary surface hairs (Fig. 18, a). 

2. Plumose natatory hairs (Fig. 18, V). 

Those under which the chitinous integument is per- 



SENSE-HAIRS. 



17 



forated, and a special nerve-fibre runs to the base of the 
hair. 

1. Hairs solid. 

(1) Hairs attached stiffly ; organs of touch 
(Fig. 18, e). 

(2) Hairs attached by means of a thin mem- 

brane, sometimes plumose ; organs of hear- 
ing (Fig. 18, <2>. _ 

2. Hairs hollow, and either open at the end, or 
closed by an extremely delicate membrane. 

(1) Hairs containing a continuation of the 

nervous plasma ; 
organs of smell 
(Fig. 18, e). 

(2) Hairs generally 
very short, and 
situated in tlie 
mouth or on the 
mouth part ; or- 
gans of taste 
(Fig. 18,/). 

Each of these classes 
is again subject to end- 
less modifications, and 
others will doubtless here- 
after be discovered. The 
sense-hairs are also often 
more or less completely 
sunk in the chitinous in- 




tegument. 



Fig. 19. — Part of the proboscis of a fly 
(Musca); after Leydig. n, Nerve; g, 
ganglionic swellings ; s, tactile hairs or 
rods; c, cuticle. 



Fig. 19 shows some of 
the tactile hairs on the proboscis of a fly (Musca), each 
seated on a ganglion and connected with a nerve (n). 



18 



TACTILE HAIRS. 



The tactile hairs — as, for instance, those on the upper 
side of the proboscis of the fly — are delicate, hollow, 
tapering, pointed organs, inserted on a chitinous ring, 
and connected with a nerve which immediately below 
the skin swells into a multicellular ganglion. 




Fig. 20.— Right half of eighth segment of the body of the larva of a gnat (Corezhra 
plumicornis) ; after Graber. E, G, Ganglion ; W, nerve ; g, auditory ganglion : 
gb, auditory ligament; Ch, auditory rods; a, auditory nerve; e, attachment of 
auditory organ to the skin; b, attachment of auditory ligament; hn, hn', termi- 
nation of skin-nerve; tb, plumose tactile hair; h, simple hair; tg, ganglion of 
tactile hair ; Im, longitudinal muscle. 

The terminations of the nerves and their connection 
with the sensitive hairs are also beautifully shown in 
some of the transparent water-insects. Fig. 20 repre- 
sents part of one segment of the glassy larva of a gnat 
(Corethra plumicornis), showing the tactile hairs (Fig. 
20, A, tb), and the nerves connecting them with the 
central ganglion (Fig. 20, EG). 



CHAPTER II. 

THE SENSE OF TASTE. 

While the organs of touch are spread more or less over 
the whole surface, and those of sight and of hearing 
may be, and in fact are, situated in very different parts 
of the body in different animals, the sense of taste is 
naturally confined to the mouth or its immediate 
neighbourhood. 

In the case of Man, it resides especially in the tip, 
the edges of the upper surface, and the back part of the 
tongue, and (probably) the inferior portion of the soft 
palate. The actual mode of termination of the nerves 
of taste has, however, only recently been discovered. 

Loven and Schwalbe detected, independently and 
almost simultaneously, in the epithelium of the papillae 
of the tongue, many small budlike groups of cells (Fig. 
21) which are probably connected with the ultimate 
fibres of the glosso-pharyngeal nerves. These have 
been supposed to be the special seats of the sense of 
taste, and thence termed "taste-buds;" they are in 
man shaped like a flask, in some other animals they are 
more slender. In the dog, they are 072 of a millimeter 
in length, and '03 in breadth. 

In the pig the number is estimated at 9500 ; in the 
sheep, at 9600; in the rabbit, at 1500 ; in the cow, at 



20 



TASTE-ORGANS OF MAN. 



35,000. In man they almost touch each other on some 
parts of the tongue, and their number is very great. 




Fig. 21.— Taste-Buds of the rabbit (after Engehnann in Strieker's "Handbook"), x 450. 

The "taste-buds" consist of from fifteen to thirty 
long narrow cells, arranged almost like a circular bundle. 
Those on the outside lie in close contact with the walls 
of the cavity. The cells appear to be of two kinds : 





Fig. 22. — a, Isolated taste-cells from the mouth of rabbit ; b, two cover-cells and a 
taste-cell in their natural position (after Engelmann), x 600. 

the outer ones do not differ markedly in appearance — 
at least, with our present magnifying powers — from 
ordinary epithelial cells, and have not been shown to 
be connected with nerves. Those in the centre are 



MAMMALIA— BIRDS— REPTILES. 



21 



more highly organized. Each consists of an ellipsoidal 
nucleus surrounded by a thin layer of protoplasm, 
continued downwards into a fine fibril, which sometimes 
branches, and which — though this is not clear — probably 
joins the nervous fibres. The upper process of the 
protoplasm is a narrow cylinder, in some cases prolonged 
at the end into a very delicate hair or rod. 

Schwalbe thought he could distinguish in man and 
the sheep, two kinds of taste-ceils — firstly, needle cells, 
in which the cell appears to terminate in a narrow, 
brilliant needle, abruptly cut off at the end ; and, 
secondly, staff cells, which are less numerous, shorter, of 
uniform breadth, and without 
any terminating needle. It is 
still unknown whether there are 
different classes of taste-cells 
for different tastes, and whether 
one taste-bud can distinguish 
more than one taste. 

I know of no detailed de- 
scription of the organs of taste 
in birds and reptiles. In the 
frog the taste-organs are not 
flasklike, but are flat disks. 
They occur in hundreds on the 
tongue and soft palate. These 
taste-disks are composed of 
several forms of cells. Those 
which are supposed to be espe- 
cially connected with the sense 
of taste terminate in a fork, sometimes, though rarely, 
of three prongs. The taste-organs of fishes are shaped 
like beakers. 




Fig. 23. — Termination of the 
nerves of taste in the frog, 
showing the ramifications of 
the nerve-fibres and their con- 
nection with the cells of taste 
(after Engelmann), x 600. 



22 TASTE-OKGANS OF THE LOWER ANIMALS. 



It will be observed that these structures give us no 
help to realize in what actually consists the sense of 
taste. We know that we possess it ourselves. We 
perceive that other animals can select, and appear to 
enjoy, their food, and hence we ascribe to them a 
similar faculty. We know that in our own case this 
sense resides in the mouth, and we assume that it 
must do so in other animals; we find in the mouth 
certain structures, and we infer that to them is due 
the sensation of taste. Even in our own case the 
inferences are, perhaps, not very clear, and certainly the 
facts, as yet known, aid us but little in framing any 
definite idea of the process. 

But if our knowledge is so imperfect in the case of 
the higher animals, it becomes much more so in the 
lower groups. 

In the Mollusca, Annelida, and lower groups, we know 
scarcely anything of the organ of taste, though we 

can hardly doubt that such 
exists. 

Medusae (jelly-fishes) are 
very sensitive to any change 
in the composition of the sea- 
water ; for instance, they sink 
below as soon as it begins to 
rain. It is difficult, however, 
to say which sense is affected. 
In Asterope (a marine worm 
belonging to the Alciopidae), 
Greef has described, in the 
skin of the proboscis, certain 
ppculiar club-shaped, ringed bodies, which taper into a 
thread connected with a nucleated cell. These he 




Fig. 24. — Inner layer of the skin 
of the proboscis of Asterope Can- 
dida, x 400 Tafter Greef). a, 
Cuticle ; b, terminal (nerve) 
organs; c, ganglionic cells; d, 
longitudinal muscl? ; e, trans- 
verse muscle. 



CRUSTACEA— INSECTS. 23 

suspects to be ganglionic cells, and he suggests that the 
organ is one of taste. 

Even in the Crustacea (crabs, lobsters, etc.), though 
we can scarcely doubt that they possess the sense of 
taste, no organs have been yet described to which it 
can be with any confidence ascribed. Huxley, for 
instance, in his work on the Crayfish,* says, "It is 
probable that the crayfish possesses something ana- 
logous to taste, and a very likely seat for the organ of 
this function is in the upper lip and the metastoma, but 
if the organ exists it possesses no structural peculiarities 
by which it can be identified." 

As regards insects, the possession of the sense of taste 
cac not be questioned, though, except perhaps in many 
Hymenoptera and certain phytophagous insects, it may 
not be of great importance. No one who has ever 
watched a bee or a wasp can entertain the slightest 
doubt on the subject. It is, again, probably by taste 
that caterpillars recognize their food-plant. Moreover, 
this is partly the effect of individual experience, for, 
when first hatched, caterpillars will often eat leaves 
which they would not touch when they are older, and 
have become accustomed to a particular kind of food.f 
Special experiments, moreover, have been made by 
various entomologists, particularly by Forel and Will. 
Forel mixed morphine and strychnine with some honey, 

* "The Crayfish : an Introduction to the Study of Zoology." 
f A remarkable case is afforded by those species in which the food of 
the larva and perfect insect is different, so that the mother has to select 
and find for her offspring food which she would not care to touch her- 
self. Thus while butterflies and moths themselves feed on honey, each 
species selects some particular food-plant for the larvse. Again, flies, 
which also enjoy honey themselves, lay their eggs on putrid meat and 
other decaying animal substances. 



24 SENSE OF TASTE IN INSECTS. 

which he offered to his ants. Their antennae gave them 
no warning. The smell of the honey attracted them, 
and they began to feed; but the moment the honey 
touched their lips, they perceived the fraud. Will tried 
w 7 asps with alum, placing it where they had been accus- 
tomed to be fed with sugar. They fell into the trap, 
and ate some, but soon found out their error, and began 
assiduously rubbing their mouth parts to take away the 
taste. 

Will found that glycerine, even if mixed with a large 
proportion of honey, was avoided ; and to quinine they 
had a great objection. If the distasteful substance is 
inodorous and mixed in honev, the ant or bee com- 
mences to feed unsuspiciously, and finds out the trick 
played on her more or less quickly according to the 
proportion of the substance and the bitterness or 
strength of its taste. 

The delicacy of taste is, doubtless, greater in bees 
and ants than in omnivorous flies or in carnivorous 
insects. At the same time, the sense of taste in ants is 
far from perfect, and they cannot always distinguish in- 
jurious substances. Forel found that if he mixed 
phosphorus in their honey, they swallowed it unsus- 
pectingly, and were made very unwell. Some workers, 
he says,* " de Formica pratensis se gorge rent de miel au 
phosphore que je leur donnai. Apres cela elles 
demeurerent pendant de nombreuses heures immobiles, 
les mandibules ecartees, la bouche ouverte, avec l'air 
tres obsedees. Celles qui en avaieiit le plus mange 
perirent, les autres guerirent peu a pen." It cannot, 
then, be doubted that insects possess a sense of taste, 
the seat of it can hardly be elsewhere than in the 
* " Eeceuil Zool. Suisse." 1887. 



ORGANS OF TASTE IN INSECTS. 25 

mouth or its immediate neighbourhood; and in all the 
orders of insects there are found on the tongue, the 
maxillae, and in the mouth, certain minute pits which 
are probably the organs of taste. In. each pit is a 
minute hair, or rod, which is probably perforated at 
the end. On this point there is, indeed, some dif- 
ference of opinion. Will, for instance, maintains 
that to convey the sense of taste the food must come 
into direct contact with the termination of the nerve 
of taste, so that those hairs, or bristles, on the mouth 
parts which present no perforation cannot be regarded 
as true taste-organs, and probably serve rather as 
guards. Forel, on the contrary, considers this as an 
error. He observes, with justice, that the secretions 
are able to pass through the chitinous membrane 
which terminates the excretory canals of the glandular 
cells, and he maintains that the chitin is so thin 
and delicate — as well on the surface of the taste cones 
and hairs as on the olfactory hairs and plates of the 
antennae of bees and other insects— that endosmosis 
through this fine membrane may sufficiently explain 
the sensation. 

In 1860 Meinert* described, on the maxillae and 
tongue of ants, a series of chitinous canals, connected 
with ganglion cells, and through them with the nerves, 
and suggested — though with a note of interrogation — 
that they might be the organs of taste. Forel, in 1874, 
confirmed these observations of Meinert's, and described, 
at the point of the tongue of Formica pratensis, a series 
of seven such chitinous tubes. In the following year 
Wolff published his work, "Das Riechorgan der Biene," 
which contains a number of valuable observations, 
* " Bid. til. de Danske Mvrers Natur Hist." 1860. 



26 THE BEE. 

though I am unable altogether to concur in his con- 
clusions. He described a group of minute pits at the 
base of the tongue of the bee, and considered them 
as the organs of smell. It seems to me, however, more 
probable that they serve as organs of taste. Forel * 
also is disposed to regard these as constituting, perhaps, 
the most important part of the organ of taste, but con- 
siders that this sense resides also in certain organs 
scattered over the tongue and the maxillae. Will 
regards the maxillae and tongue as the only organs of 



^Sk 




^"-£ju_ 



Fig 25 — Taste-organ of the bee (after Wolff) B, Horny rir'ge; 7?, R, sensory pits, 
C, C, skin of the mouth ; L, muscular fibres ; A, A, muscular fibres ; S, 5", a b c 
d ef, section of skin of oesophagus. 

taste in the bee. He maintains f that the organs of 
"Wolff are deficient in the first requisite of an organ of 
taste, for that there is no orifice through which the food 
could directly enter into relation with the nerve. 

No doubt, moreover, the taste-organs on the 
tongue and maxillae might be of themselves suffi- 
cient, so that a priori wo need not seek for any 
others. At the same time, as to the existence of the 

* " Sensations des Insectes," Receuil. Zool. Suisse, 1887. Kraepelin 
also regards them as the organ of smell. 

t Will, " Das Geschmacksorgan der Insekten," Zeit, fur Zool, 1855. 



HYMENOPTERA. 



27 



organs described by Wolff there is no doubt, and 
their position certainly seems to indicate that they 
are organs of taste. Moreover, we are not, I think, 
sufficiently acquainted either with the essential 
requisites of an organ of taste, on the one hand, or, ou 
the other, with the minute structure of these organs, to 
feel justified in concluding that this is impossible. It 
must be remembered that these pits are very minute, 
being only from *003 to '006 of a millimetre in diameter, 
so that it is hazardous to assert that they are certainly 
imperforate, while even if they are, 
this would not necessarily prove 
that they cannot be organs of taste. 

Fig. 26 shows three of Wolff's 
cups, each with a central hair, a 
chitinous ring, and a double gan- 
glionic swelling terminating in a 
nerve-fibre, magnified 500 time.*. 

An additional reason for sup- 
posing that the Wolffian pits are 
really sense-organs arises from the 
fact that they are fewest in those 
insects which we may reasonably 
suppose to have the sense of taste least developed, 
and increase in number where, on other grounds, we 
may fairly regard it as being probably more highly 
developed. Thus the Chalcididse have often only one 
or two; the Evaneadae, seven; the Proctotrupidge, 
fifteen ; the Tenthredos, twelve to twenty-four ; the 
common wasp, twenty : some of the great tropical wasps, 
forty ; while in the hive bee, the drone has fifty, the 
queen about one hundred, and the worker rather more 
still, say one hundred and ten. 




Fig. 26. — Shows three of 
Wolff's cups, each with a 

central hair, a chitinous 
ring, and a double gangli- 
onic swelling terminating 
in a nerve-fibre, x 500 
times. R, R', Sensory pits 
and hairs; G. G, ganglionic 
swelling of nerve. 



28 



HUMBLE BEE — WASP. 



Kraepelin has described at the end of the proboscis 
in the humble bee (Bombus), besides the hairs of touch, 
certain peculiar club-shaped hairs, which he believed 
were perforated at the end, and which he considered to 
be taste-hairs ; and Haller has ascribed the same 
function to some very similar hairs which he found on 
the under lip of the Hydrachna. 





Fig. 28. — Section through a taste- 
cup (after Will). SK, Support- 
ing cone; N, nerve; SZ, sense- 
cell. 



Fig. 27.— Under side of left maxilla of 
Vespa (after Will). Gm y Taste-cups , 
Shm, protecting hairs; Tb, tactile hairs ; 
Mt, base of maxillary palpus. 

Fig. 27 represents the under side of the left maxilla of 
a wasp (Vespa vulgaris), after Will, magnified 55 times. 
Om are the taste-cups; Shm, the protecting hairs; 
Tb, the tactile hairs. 

Fig. 28 represents a section through one of the taste- 
cups, 8k is the taste-cone contained in the cup ; it is 
perforated and continuous at the base with a nerve-fibre. 



FLY. 



29 



Similarly, in the wonderfully beautiful and complex 
proboscis of the hive bee there is, between each of the 
trachea-like ducts, a row of minute pits (Fig. 29, Gs), 
with a central papilla, which have been described by 
Leydig, Meinert, Lowne, Kraepelin, and others, and 
are probably organs of taste. 

Kraepelin * distinguishes four kinds of hairs on the 
proboscis of the fly : 

1. Ordinary hairs, which are not hollow, and do not 
stand in connection with a nerve. 

2. Hairs of touch. These are 
principally situated on the upper 
side. They are delicate, hollow, 
pointed organs, situated on a ring 
of the integument, and connected 
with a nerve. 

3. Glandular hairs. These are 
larger than the former, and the 
chitinous ring is sometimes so much 
developed as to form a short cylin- 
der surrounding the base of the 
hair. The principal characteristic 
is, however, that the hair presents 
along one surface a deep furrow, 
and is connected at the base with a cellular organ. 
Kraepelin therefore considers that this is a gland, and 
that the secretion passes outwards along the furrow. 
Kunckel and Gazagnaire, however, regard these also as 
sense-hairs. The supposed gland they consider to be 
a ganglion. 

4. Taste-organs (Fig. 30). These lie in a row between 

* Kraepelin, " Zur Anat. und Phys. des Kiissels von Musca," Zeit. 
fur Wiss. Zool, 1883. 




Fig. 29.— Tip of the probos- 
cis in the hive bee (Apis), 
X 140. L, Terminal 
ladle ; Gs, taste-hairs ; 
Sh, guard-hairs ; Rb, 
hooked hairs. 



30 



FLY. 



the trachea-like channels, and correspond to the similar 
organs in the bee (Fig. 29, Gs). Each of these resembles 
a double circle, which scarcely projects, if at all, beyond 
the general surface, and which he regards as a 
metamorphosed, hollow, perforated hair. At the base 
of each organ is a nerve, which at some little distance 
forms a multicellular ganglion, and the 
sheath of which, immediately below the 
skin, forms a delicate and short, but well- 
marked, chitinous, cylinder. 

It may also be observed, at any rate in 
most insects, that while they are feeding 
the palpi hang down motionless, and evi- 
dently take no part in the operation. 

In reference to the sense of taste, I may 
also mention that an additional complexity 
arises from the fact that many insects 
possess more than one kind of salivary 
gland, and it is possible, as Wolff sug- 
gests,* that the secretions may have dif- 
ferent properties. In addition to this, 
Wolff thinks he has proved that the 
character of the secretion differs at differ- 
ent ages; that for many days after the 
bee has arrived at its imago condition, 
the glands are still imperfect and gradually 
increase to their full size. In old bees, 
again, according to him, the secretion diminishes in 
quantity. This, perhaps, throws some light on the 
division of labour. Forel has observed among ants 
that they remain for some days engaged in indoor 




Fig. 30. — Organ 
of taste of fly 
(JIusca vomi- 
toria) ; after 
Kraepelin. gn, 
Nerve ; gg, gan- 
glion ; ax, axe- 
cylinder ; gc, 
terminal cylin- 
der ; gk, termi- 
nal cone. 



* " Das Riechorgan der Biene." 



INDIVIDUAL DIFFERENCES. 31 

duties, and do not leave the nest till some time after 
they have arrived at maturity. 

I have noticed, also, that some individuals seem to 
possess a finer sense of taste than others, and some light 
seems to be thrown on this difference by the fact that 
the number of the taste-pits is not the same in all indi- 
viduals. Thus Will observed that the number on the 
tongue of Lasius flavus (our common yellow ant) varies 
from twenty to twenty-four, and in Atta from forty to 
fifty-two. The number of pits on the maxillae is subject 
to still greater variations, and is not even always the 
same on the two sides of the same insect. 

On the whole, then, we may conclude that the organs 
of taste in insects are certain modified hairs situated 
either in the mouth itself or on the organs immediately 
surrounding it* 



CHAPTEE liL 

THE SENSE OF SMELL, 

The organ of smell is, in vertebrate animals, embedded in 
the mucous membrane of the nostrils, and in mammalia 
can generally be distinguished by its yellow or brownish 
colour. In birds, on the contrary, it presents hardly 
any peculiarity to the naked eye. For our knowledge 
of the minuter structure w r e are mainly indebted to 
Max Schultze. The cylindrical epithelial cells in the 
olfactory organs of man (Fig. 31) terminate in broad flat 
ends. Between them are rod-like filaments, which are 
supposed to expand into a, ganglionic cell, terminating 
in a nerve-fibre. Schultze terms these olfactory cells. 

In other cases, as in birds, Amphibia (Fig. 32), etc., 
the olfactory cells terminate in fine cilise, or olfactory 
hairs, either one or many to each cell. These hairs 
are sometimes motionless, sometimes have a slight 
movement of their own. It is obvious that no one from 
the structure alone could have predicated the function ; 
nor can we, I think, form to ourselves any satisfactory 
conception how such a structure conveys the impression 
of smell, or in what consist the differences between 
different odours. 

If, then, we know really so little as to the mode, or 
organs, by which the sense of smell is induced among 



PROTOZOA AND CCELENTEEATA. 



33 



the higher animals, we cannot wonder that in the 
lower groups our knowledge is still less. 

In the Protozoa and Coelenterata no organs have yet 
been met with to which this function can with any 
confidence be ascribed. 




Fig. 31.— Epithelial 
and (B) olfactory- 
cells of man (from 
Strieker, after 
Schultze). 




Fipr. 32. — Cells from the olfactory 
region of a proteus (after Strieker). 
a, Epithelial cells ; b, the apparent 
processes; c, olfactory cells. A, 
Cilia?. 



Meyer has described,* in Polyophthalmus (a small 
marine worm), on each side of the head, two ciliated 
organs (Fig. 33), which have been supposed to be organs 
of smell. These had been already mentioned by 

* " Zur. Anat. imd Hist, von Polyophthalmus, 5, Arch, fur Mic. 
AnaL, 1882. 



34 WORMS— MOLLUSCA. 

De Quatrefages, who compared them with the ciliated 
wheels of Kotifers, and thought that they produced 
currents in the water, thus urging microscopic algae, 
infusoria, etc., to the mouth of the worm. Meyer, on 
the contrary, with more probability, regards them 
as olfactory organs. They are slight depressions 
(Fig. 33) in the general surface, lined with peculiar 
long cilise, supplied with a large nerve coming from 




Ttp.dx. 



Fig. 33.— Section through the head segment of Folyophthalmus. x 300 (after Meyer). 
Imd, muscle ; bo, cup-shaped organ ; cu, cuticle ; hp, hypoderm ; Imd, longitu- 
dinal dorsal muscle ; n, peripheral nerve ; cz, commissure of brain ; mb, mem- 
brane ; pgn, pigment-cells ; hpdz, unicellular glands in the hypoderm ; gn, brain ; 
Tc, nuclei in the brain. 

the cerebral ganglion gn. Similar pits occur in many 
other Annelida. They differ in number; Polyoph- 
thalmus having only a pair, the Capitellidse several. 

In the Mollusca, the hinder pair of tentacles have 
been supposed by some to serve as olfactory organs. 
In the cuttle-fish (Cephalopoda) there are certain pits, 
at the base of which is a papilla, supplied with a nerve, 
which is perhaps olfactory.* The true function of the 
* Leydig, " Histologie." 



INSECTS— SEAT OF THE SENSE OF SMELL. 35 

organs described by Hancock in Gasteropoda, and by 
Leuckart in Pteropods, as olfactory, seems very doubtful. 

As regards the seat of the sense of smell in insects, 
there have been four principal theories. It has been 
supposed to reside — (1) In the spiracles, or breathing 
holes ; (2) in the neighbourhood of the mouth ; (3) in 
the antennae ; (4) in different parts of the body. The 
history of the question has been well given byKraepelin 
in an admirable memoir, " Ueber die Geruchsorgane 
der Gliederthiere." * 

Sulzer, in 1761,f suggested that the organ of smell 
was probably to be found in the neighbourhood of the 
spiracles, or breathing-holes. It is hardly necessary to 
observe that insects do not breath as we do, through 
their mouths, but through a series of orifices along the 
sides, leading into tracheae, or air-tubes, which ramify 
throughout the body ; so that the blood is aerated, not 
in one special organ, but throughout its course. Now, 
it is important that a more or less continuous current 
of air should pass over the surface of the organ of 
smell, as it is in this manner brought in contact with 
the odoriferous particles. In man and the other air- 
breathing vertebrates, the combination of the entrance 
to the lungs with the nose and mouth offers great 
advantages. The olfactory organ is brought close to 
the mouth, where it is especially useful in the exami- 
nation of food ; while the continuous current of air 
necessary to respiration is utilized in the production 
of sound, on the one hand, and in bringing odoriferous 
particles to the organ of smell, on the other. 

* Separat Abdruck aus deni Osterprogramm der Kealschule des 
Johanneum." 1883. 

t " Gesehichte der InsekteD." 



36 DIFFERENT THEORIES AS TO 

In in sects the separation of the mouth from the 
respiratory orifices is, in this respect, a manifest dis- 
advantage. Still, it was not unnatural to look for the 
organ of smell in the neighbourhood of the spiracles, 
Sulzer's view was supported by Yon Keimarus, Baster, 
Dumer.il, Schelvir, and especially by Lehmann,* who 
lays it down as a general proposition that every organ of 
smell is to be sought near the orifices through which 
animals breathe : " Omnibus olfactus organon in iis 
locis quserendum est, per quos inspirent." 

The most careful observations, however, have failed 
to detect in the neighbourhood of the spiracles any 
special supply of nerves, or any organ which could be 
supposed to serve for the perception of odors, and I 
believe this view may be said to be now generally 
abandoned, t 

Treviranus $ suggested that the organ of smell was 
situated in the mouth, and he has been followed by 
Newport, Wolff, Kirby and Spence, and Graber. The 
descriptions they have given may be accepted as 
correct, but the organs they describe in the mouth 
itself are rather, I think, to be ascribed to the sense 
of taste than to that of smell. 

Lyonnet, Bonsdorff, Marcel de Serres, Newport, and 
others, believed that the sense of smell resides in the 

* Lehmann published three memoirs on the subject : " De Sensibus 
Externis Animalium Exsanguium," 1798; "De Antennis Inseetorum 
Dissertatio," 1799; and "De Antennis Inseetorum Dissertatio Pos- 
terior;' 1800. 

t Joseph, indeed (" Bericht der 50 Vers. Deutscher Nat. und Aerzte. 
Miiuchen," 1877), supported this view in a short communication, and 
has promised fuller details. These, however, have not, I believe, yet 
appeared. 

X "Ueber das Saugen und das Geruchsorgan der Insekten," Ann, 
der Wetter Ges., 1812. 



THE SEAT OF THE SENSE OF SMELL. 37 

palpi, although the experiments of Perris, Plateau, 
Forel, and others, have conclusively proved that it 
is not situated exclusively in them. 

The credit has been ascribed to Keaumur of having 
been the first to suggest that the sense of smell is 
seated in the antennae. This view has been adopted 
by Lesser, Boesel, Lyonnet, Bonnet, Sulzer, Latreille, 
Burmeister, Lefevre, Erichson, Duges, Perris, Dufour, 
Slater, Vogt, Forel, Lowne, Hauser, Kraepelin, Schie- 
menz, and other observers, and my own observations 
lead me to the same conclusion. 

Many entomologists, indeed, including Scarpa, Schnei- 
der, Bolkhausen, Bonsdorff, Carus, Strauss-Durckheim, 
Oken, Kirby and Spence, Newport, Landois, Hicks, 
Wolff, and Graber, have considered that the antennae 
serve as ears. These two views are, however, not 
irreconcileable, and the truth seems to be that, while 
organs of smell and of hearing, when present, may be 
both situated in the antennao, they are not in all cases 
confined to them. 

Comparetti * seems to have been the first to suggest 
that the organ of smell might not be seated in the 
Game part of the body in all insects ; he suggested the 
antennae in certain beetles (Lamellicornia), the pro- 
boscis in butterflies and moths (Lepidoptera), and 
certain frontal cellules (the existence of which has, 
however, not been confirmed) in locusts, etc. (Orthop- 
tera), as the probable seats. 

The real manner in which odors are perceived, and 
the structure of the olfactory organs, is still so little 
understood, that experiments are perhaps more con- 
clusive than anatomy. 

* " De aure interna comparata-Patavii." 1789. 



38 EXPERIMENTS. 

The oldest experiments of importance are those of 
Lehmann. He bored holes through bottles, and then 
inserted into them the abdomen of various insects, filling 
up the interspace with wax, and leaving the head and 
thorax outside. He then introduced into the bottle 
various powerful odors, such as burnt feathers, assafoe- 
tida, burnt sulphur, etc., and as these caused obvious 
movements of the body, he concluded that the insects 
perceived the smell by the membrane surrounding the 
tracheae The facts have been verified by subsequent 
observers, and are themselves doubtless correct. They 
do not, however, prove Lehmann's case, for similar fumes 
would, as Duges and Perris justly observe, produce an 
irritation in our throat, where there is certainly no 
sense of smell. On the other hand, when substances 
which have no such irritating properties are used, as, 
for instance, honey in the case of a bee, decaying meat 
with a carrion-eating beetle (Silpha), and so on, no re- 
action has been perceived. On the whole, experiments 
lend no countenance to Sulzer's theory (see p. 35), 
and, in the absence also of any anatomical evidence 
in its support, it has, I believe, now no advocates. 

I pass, then, to the second theory — that which 
considers that the organ of smell is situated in the 
mouth parts, either in the mouth itself according to 
some authors, or the palpi according to others. We 
have, I think, no clear evidence that the mouth itself 
possesses any organ of smell. Huber, however, observed 
that while, if he brought close to the mouth of bees 
substances which were repulsive, or others which 
were acceptable to them, such as honey, they were evi- 
dently affected ; this was, on the other hand, no longer 
the case if the mouth parts w r ere stopped up with paste. 



EXPERIMENTS WITH D1NETUS. 39 

Perris, on the contrary, found that even when the 
whole of the mouth parts were enclosed in gum, insects 
still retained the power of smell. These observations 
have been entirely confirmed by Forel and other 
observers. The explanation, I believe, is that Corn- 
paretti was right, and that the sense of scent is not 
confined to one part of the body; that, while it is pos- 
sessed by the palpi, it is not confined to them. 

It has long been observed that insects use their 
antennsG to exarniue and test their food. This is clearly 
not an act of hearing ; nor has any one suggested that 
the antennae are organs of sight or taste. It is obviously 
more than mere touch — indeed, they do not need to 
come into actual contact — and is, therefore, probably 
that of smell. 

This conclusion has been confirmed by many experi- 
ments. Among those of the older observers some of the 
most important were made by Perris.* In Dinetus, a 
genus of the solitary wasps, the female, when absent in 
search of prey, covers over the orifice to her nest with a 
little sand. Perris selected two nests, and while the 
wasps were absent he disturbed the surface round one 
nest with a piece of stick, and laid his hand (which was 
rather warm) over the other. The first Dinetus was a 
little disturbed. She ran about, rapidly vibrating her 
antennae, and was, perhaps, rather longer than usual in 
finding the entrance, but lost very little time. The 
other, he says, " Se trouva de prime abord, beaucoup 
plus embarrasse : ma main, dont l'etat de moiteur avait 
rendu les emanations beaucoup plus actives, avait 
laisse sur le sable une odeur qui semblait Tetonner, et 

* "Sur le siege de l'odorat daus les articules," Ann. Set. Nat, 
1850. 

4 



40 EXPERIMENTS WITH HYDATICUS. 

qu'il cherchait a reconnaitre : car lorsqu'il arrivat a 
1'endroit que ma main avait convert, il ralentissait sa 
marche, et ses antennes palpaient rapideinent le sable. 
Le pauvre insecte s'epuisait en marches et contre- 
marches ; il passait par dessus son nid sans s'en douter ; 
il crensait 9a et la avkc ses pattes de petites fosses, dans 
lesquelles il plongeait ses antennes pour explorer les 
couches inferieures; il s'arretait pour brosser ses 
antennes, comme on se frotte les yeux quand on se 
sent ebloui : rien n'y faisait. Decourage, il prit son 
vol ; mais il revint quelques instants apres et recom- 
menpa ses recherches. Cette fois, soit qu'il fut mieux 
dispose et que les antennes qui etaient evidemment 
l'agent explorateur, fussent plus perspicaces, soit plutot 
que le soleil qui etait ardent eut fait evaporer les 
emanations de ma main, il parvint retrouver son nid, 
mais il y mit bien du temps et de la patience." 

Perris also repeated Lehmann's experiment, only 
that he inserted the head of the insects into the bottles 
instead of the body; he then satisfied himself that 
they perceived odors, and hence concluded that the 
sense of smell resides in the head, partly in the antennae, 
and partly in the palpi. 

Newport, on the contrary, maintained that the 
antennae possess no sense of smell. He experimented 
on a water-beetle, Hydaticus cinereas, which, he says, "I 
had purposely confined for three days without food in 
a cup about half filled with water, and, at the expiration 
of that time, attached a small piece of raw flesh to the 
end of a wire, and carried it several times along the 
sides of the insect, particularly near the spiracles, where 
it was suffered to remain for a short time. The insect, 
however, did not appear to perceive it, but during the 



EXPERIMENTS WITH SILPHA. 41 

whole time remained in the water perfectly undisturbed. 
The flesh was then carried very near to one of the 
antennae, but without exciting the slightest motion in 
that organ, while the insect began to move its palpi 
very briskly, as if it detected the presence of something; 
but continued, in other respects, motionless as before. 
The flesh was then brought in direct contact with the 
antennae, and the insect immediately withdrew them as 
if annoyed, as in the experiment with the Silpha. It 
was then carried exactly in front, and at abuut the 
distance of an inch. The palpi were instantly in rapid 
motion, and the creature, darting forward, seized the 
"flesh, and began to devour it most voraciously. The 
following day the experiment was repeated several 
times, and with precisely the same result ; but on this 
occasion the antennae were so repeatedly touched with 
the flesh, that the annoyed insect kept them at last 
beneath the sides of the thorax. Hence I think it 
must appear that, from there being no alterations in 
the motions of the insect when the food was held 
near the sides of its body, the sense of smelling does 
not reside in the spiracles, nor, for like reasons, in 
the antennae ; while, from the motion of the palpi 
and the avidity with which the insect darted upon the 
food when held in front of it, it seems but fair to con- 
clude that the sense of smelling must certainly reside 
in the head, as above suggested." * 

Again, he took a Silpha (one of the carrion-eating 
beetles), and, " placing it in a glass, attached a 
small piece of flesh within half an inch of it. The 
antennae, as is usual with these insects, continued to 

* Newport, " On the Antennse of Insects," Transactions of the Ento- 
mological Society, 1837-1840. 



42 EXPERIMENTS WITH SILPHA. 

be moved about on either side, but with nothing 
remarkable in their motions, while the head of the 
insect was a little elevated and carried forwards, as if it 
perceived the flesh, and the palpi were in rapid vibra- 
tory motion. It soon approached very near to the food, 
and at length touched it three or four times with the 
antennae, but each time suddenly withdrew them as if 
they had fallen unexpectedly on something obnoxious, 
the palpi during the whole time continuing their motion. 
The insect at length reached the food, and, after having 
touched it once or twice with the extremities of the 
palpi, their motion ceased, and it commenced feeding, 
while the antennae were occasionally in motion as 
before." It would certainly seem, therefore, that in 
these insects, at any rate, the sense of smell resides 
principally in the palpi. 

Newport made certain other experiments on the 
powers of hearing of insects, which I shall mention in 
the next chapter, and he concludes, " These facts, 
connected, with the previous experiments, have con- 
vinced me that the antennae in all insects are the 
auditory organs, whatever may be their particular 
structure, and that, however this is varied, it is appro- 
priated to the perception and transmission of sound." 

Newport was an excellent observer and profound 
entomologist, and I see no reason to doubt the correct- 
ness of his observations ; nor, indeed, of his inferences, 
so long as we confine them to the species on which the 
observations were made. Tbey may prove that some 
insects possess no sense of smell, or that, at any rate, 
it does not reside in the antennae. On the other 
hand, they cannot disprove the positive results obtained 
by other observers, that in other species the opposite is 



EXPERIMENTS WITH STAG-BEETLE, ANTS. 43 

the case, and that in them the sense of smell does 
reside in the antennae. 

That the stag-beetle can smell seems clearly proved, 
but Landois found * that, after the removal of the 
terminal plates of the antennae, the insect still possessed 
this faculty, whence he concluded that the sense of 
smell must reside in some other part of the body, and 
that the antenna? probably serve as organs of hearing. 
This does not, however, prove that the sense of smell 
does not reside partly in the antennae. 

Forel removed the palpi and mouth parts of a wasp, 
and she appeared to perceive the presence of honey as 
well as before. 

I myself took a large ant (Formica ligniperda), and 
tethered her on a board by a thread. When she was 
quite quiet, I tried her with tuning-forks ; but they 
did not disturb her in the least. I then approached the 
feather of a pen very quietly, so as almost to touch 
first one and then the other of the antennae, which, 
however, did not move. I then dipped the pen in 
essence of musk and did the same ; the antenna was 
slowly retracted and drawn quite back. I then repeated 
the same with the other antenna. I was, of course, 
careful not to touch the antennae. I have repeated 
this experiment with other substances with several 
ants, and with the same results. Perris also made the 
same experiments with the palpi, and with the same 
result ; but if the palpi were removed, the rest of the 
mouth gave no indications of perceiving odours. 

Graber f also has made a number of experiments, and 

* "Das Gehororgan des Hirsehkafers," Arch. fur. Mic. AnaL, 1868. 
t "Vergl. Grundversuche iiber die Wirkimg und die Aufnalinie- 
stellen chemischer Keize bei den Tiiieien," Biol. Centralblatt, 1885. 



44 SEAT OF THE SENSE OF SMELL 

found that in some cases (though by no means in all), 
insects which had been deprived of their antenna still 
appeared to possess the sense of smell. But if, as we 
have, I think, good reason to suppose, the power of 
smell resides partly in the palpi, this would naturally 
be the case. 

He also tested a beetle, Silpha thoracica, with oil of 
rosemary and assafoetida. It showed its perception 
by a movement in half a second to a second in the 
case of the oil of rosemary, and rather longer — one 
second to two seconds — in the case of the assafoetida. 
He then deprived it of its antennae, after which 
it showed its perception of the oil of rosemary in 
three seconds on an average of eleven trials ; while in 
no case did it show any indication of perceiving the 
assafoetida even in sixty seconds. 

This would seem to indicate a further complication — 
not only that both the antennae and the palpi may 
possess the sense of smell, but also that certain odours 
may be perceived by the former, and others by the latter. 

Gi-aber questions some of the experiments which 
seemed to me * to demonstrate the existence of a sense 
of smell in ants.f 

* " Ants, Bees, and Wasps." 

t He says, "Da Lubbock noch hinzufugt, dass keiner, der das 
Benehmen der Ameisen unter diesen Umstanden beobachten wiirde, 
den geringsten Zweifel an ihrem Geruchsvermogen haben konnte, 
wahlte ich auch diese Methode, um zu erforschen, wie sich etwa der 
Fiihler beraubte Ameisen verbalten wiirden. Ich war nicht wenig 
iiberrascht zu finden, dass auch diese (es haudelt sich um Formica 
rufa) vor dem Eiechobjekt umkehrten. Um ganz sicher zu gehen, 
versuchte ich's aber noch mit dem gleichen Arrangement aber mit 
Weglassung des Riechstoffes, und siche da ! sie kebrten auch jetzt noch 
um ! Bei genauerer Beobachtung der von einer Ameise vom Anfang 
an auf dem Papiersteg zuriickgelegten Strecke stellte sich auch bald 



PARTLY IN THE PALPI. 45 

I fastened a strip of paper in the air by means of two 
pins, suspended over it a camePs-hair brush containing 
scent, and then put an ant at one end. She ran forward, 
but stopped dead short when she came to the scented 
brush. Graber suggests that she did so from 
giddiness, but I am satisfied that this is not so. 
Ants which habitually climb trees are not likely to 
be affected by any such sensation. In my experi- 
ments, whether the bridge was high or low, broad or 
narrow, made no difference to them. Moreover, in 
each case they stopped exactly when they came to the 
scented pencil. Again, Graber has not observed that 
I expressly stated that " after passing two or three 
times, they took no further notice of the scent ; " 
nor did they notice the camePs-hair pencil unless it 
was scented. 

As regards flies (Mu^ca), Forel removed the wings 
from some bluebottle flies and placed them near a 
decaying mole. They immediately walked to it, and 
began licking it and laying eggs. He then took them 
away and removed the antennae, after which, even 
when placed close to the mole, they did not appear to 
perceive it. 

Plateau also * put some food of which cockroaches 
are fond, on a table, and surrounded it with a low 

heraus dass es sich bei dem gewissen Umkehren lediglich um em 
versuchsweises Absciireiten oder Ausprobiren des unbekannten Weges 
handelte, oder das sich die Ameisen ahnlich benehmen wie wir selbst, 
"wenn wir etwa auf einem schwanken Brette eine tiefe Gebirgsklui't 
uberschreiten sollen." 

Graber's observation is, I doubt not, quite correct ; but his inference 
is not, I think, well founded, nor was his experiment the same as 
mine. 

* Bull, de la Soc, Ent. Belqiqiie, 1876. 



46 SEAT OF SMELL PARTLY IN ANTENNA. 

circular wall of cardboard. He then put some cock- 
roaches on the table: they evidently scented the food, 
and made straight for it. He then removed their 
antennae, after which, as long as they could not see the 
food, they failed to find it, even though they wandered 
about qnite close to it. 

On the whole, then, the experiments which have 
been made seem clearly to prove that in insects the 
sense of smell resides partly in the antennae and partly 
in the palpi. This distribution would be manifestly 
advantageous. The palpi are more suited for the ex- 
amination of food ; while the antennae are more con- 
veniently situated for the perception of more distant 
objects. 

We will now glance at the antennae and palpi 
themselves, and consider briefly the structures which 
are supposed to give the sensation of smell. For 
this three conditions are requisite : (1) an appropriate 
nerve; (2) free access to air; and perhaps, though 
this is not so clear, (3) a fluid which can dissolve the 
odoriferous substance. 

The olfactory organ in Vertebrata consists, as already 
mentioned, of a mucous membrane containing (1) 
cylindrical epithelial cells, with a broad, flat termination 
at the free end ; and (2) of rod-like filaments which, 
some little distance below the surface, swell out into 
a nut-shaped expansion, and then contract again into a 
fine thread, which is probably continuous with the 
fibrils of the olfactory nerve. 

In Insects and Crustacea the conditions are different. 
The cellular "underskiu," or hypoderm, secretes a hard, 
horny envelope, and the terminations of the olfac- 
tory nerves are enclosed in a horny tube with a 



THE ORGANS OF SMELL. 47 

terminal perforation, or project as free threads. 
They differ, again, between themselves, Insects being 
as a general rule aerial, and Crustacea aquatic. 

Erichson * has the merit of having been the first 
to support this theory by anatomical examination. 
Newport had previously mentioned the existence in 
many insects of certain pits, or "pores," closed by a 
delicate membrane, and which he regarded as the seat 
of hearing. Erichson extended his observations, and 
suggested that the pits were rather to be regarded as 
organs of smell. His descriptions were confirmed by 




Fig. 34.— Antenna of Pontella Bairdii (Lubbock). 

Burmeister, who, moreover, detected in some of these 
" pits " the presence of a small knob, or hair. 

In 1853 I called special attention to the antennae 
of certain Crustacea, distinguishing five kinds of 
hairs — (1) short, downy hairs; (2) plumose hairs; (3) 
cylindrical, tapering hairs; (4) flattened, lanceolate 
hairs ; (5) wrinkled hairs — and pointed out that they 
were by no means scattered indiscriminately, but 
arranged in definite situations, indicating special 
functions. The two last I was disposed to regard 
as sense-organs. The above is a figure of the right 
male antenna of Pontella Bairdii, one of the Cope- 

* " De Fabrica et usu Antennarum in Insectis." 1847. 



48 



LEYDIG'S OLFACTORY CONES. 



poda, from one of my memoirs in that group,* and 
shows the curious clasping organ. 

Leydig, in his beautiful work on the Daphnidse, and 
more fully -in a special memoir on the subject,f de- 
scribed certain organs which had been also mentioned 
by La Vallette. I give below his figure of the 
terminal segments of one of the smaller antennae of 
the water-woodlouse (Asellus aquaticus) magnified 500 

times. It will be seen 
that there are three 
kinds of appendages — 1. 
Or d inar v stiff, cylindrical, 
tapering, pointed hairs, 
which are not connected 
with any nerve. 2. Pale, 
cylindrical hairs, with a 
blunt termination and a 
tuft of fine setae. These 
hairs are connected with a 
nerve, and Leydig regard s 
them as organs of touch. 
3. Peculiar cylinders, of 
which there is one to each 
segment. They are com- 
posed of three parts, 
the middle one somewhat 
wider than the others. The lower third is strongly chiti- 
nized, like the ordinary hairs ; the other two are more 
delicate. At the free end he observed, in some cases, 
a group of very fine, short hairs. At the base of 




Fig. 35. — Terminal segments of one of the 
smaller antenna? of the water-woodlouse 
(Asellus aquaticus), x 500 (after Leydig). 
a, Ordinary hairs (not connected with a 
nerve) ; b, sensitive hairs (with a nerve at 
the base) ; c, special cylinders (olfactory 
cylinders). 



* Ann. and Mag. of Natural History, 1853. 

t "Ueber Geruchs uud Gehororgane der Krebse und Insekten," 
Miiller's Ar., 1860. 



ORGANS OF SMELL IN CRUSTACEA — CENTIPEDES. 49 

each cylinder is a nerve, which apparently swells into 
a ganglion. 

Leydig described similar organs on the antennae 
and palpi of various other Crustacea. They have 
obviously some special function, and he suggests 
that they are olfactory organs. It is interest- 
ing that, in certain species which live in subter- 
ranean waters and have lost their eyes, these olfactory 
cones are unusually developed. They are much larger, 
for instance, in Asellus cavaticus and Gammarus 





Fig. 36.— Tip of the antenna of a centipede (Julus terrestris'), x 600 (after Leydig). 
At the apex are four olfactory cylinders, a few of which are also seen on the fol- 
lowing segment, among the ordinary hairs. 

puteanus, which live in the dark and are blind, than 
in Asellus aquaticus and Gammarus pulex or G. fluviatilis. 
Fig. 38 represents the end of the antenna of a centi- 
pede {Julus terrestris), There are four olfactory 
cylinders at the tip, and several are also seen on the 
following segment among the ordinary hairs. In this 
species the cuticle of the cylinder appeared sometimes 
as if wrinkled, and Leydig believes that the end is 
open.* Similar cylinders occur in Scolopenclra, Glo-. 

* Loc. cit., p. 286. 



50 



OLFACTORY CONES IN INSECTS. 



meris, and other centipedes. He also described similar 
cones in certain insects. 

Further details with reference to the structure and 
arrangement of these bodies have been given by Claus, 
Sars, Weissman, Rougemont, Gamroth, Heller, Hensen, 
Hauser, and others, who have also ascribed to them 
this function. In Claus's opinion, the nerve itself 
enters these bodies. On this point, however, there is 





Fig. 37. — End of a palpus of Stapliy- 
linus erythropterus, x 600 (after 
Ley dig), a, Olfactory pit. 



Fig. 38. — Part of antenna of Callianassa s>/5- 
terranea. 5, Olfactory hairs ; g, peculiar 
curved hairs. 

still much difference of opinion. At any rate, it seems 
to be established, by the most recent observations, that 
even if the cones are in some cases closed at the end, 
they certainly remain open in others. Similar organs 
also occur in the palpi (see Fig. 37). 

Kraepelin describes other peculiar forms of hairs to 
which he ascribes the perception of smell, as occurring 
in all the stalk-eyed Crustacea (Podophthalmata). 



OLFACTORY HAIRS. 



51 



These olfactory hairs are partly round (Pontonia), 
partly flat (Pagurus) ; the end is described as being 
sometimes simply open (Fig.39,a,&), sometimes provided 
with a small cone (Fig. 39, c, d, e). The number of these 
hairs is often very considerable. Moreover, they them- 
selves sometimes bear, near the base, a number of very 
fine bristles (Pagurus). There can, I think, be no doubt 
that these hairs are organs of sense, and it is probable 
that they are olfactory. The antenna of Callianassa 
(Fig. 38) also bears another remarkable series of long, 







Fig. 39.— Terminations of olfactory hairs of Crustacea, a, Of larva of a Palcemon ; 
b, of a Pagurus ; c, of a Pinnotheres ; d, of a Squilla ; e, of a Pontonia. 

thin, movable, but stiff and hooked hairs (Fig. 38, g) 9 
which also stand in direct connection with the nerve, 
and have probably some sense-function. 

In many cases the sense of smell is connected with 
minute depressions in the integument. In spiders 
Dahl has described a structure in the maxilla which he 
believes to be olfactory. The skin presents a number 
of minute orifices, under which lie elongated cells, each 
terminating in a nervous fibril.* 

Leydig also mentions f the existence of small pits on 

* "Das Gehor-und Geruchsorgan der Spinnen," Arch, fur 31ic. 
Anal, 1885. 

f "Ueber Geruchs imd Gehororgaue der Krebse imd Insekten," 
Muller's Arch., 1860. 



52 OLFACTORY PITS. 

the antennae and mandibular palpi of the crayfish 
(Astacus fluviatilis) but I do not find any further 
description of them. On the other hand, in insects they 
play a more important part, and it will be convenient 
to describe here very briefly the various structures 
occurring on and in the antennae of insects, although it 
is not to be supposed that they all serve for the sense 
of smell. Newport* alludes to the " pits" ; but they 
were first described by Erichson f ; while Burmeister % 
suggested that there are two classes — those containing 
a hair, and those in which there is none. The pits are 
only found in certain regions, and have certainly some 
specific function. In the stag-beetle (Lucanus cervus) 
the terminal plate of the antenna shows two large pits, 
one on each side, and nearly opposite one another. In 
other Lamellicorn beetles, as, for instance, in the cock- 
chafer (Melolontha vulgaris), they are very numerous. 
Lespes§ supposed them to be closed sacs, each containing 
an otolithe. They certainly do present this appearance, 
but the existence of any otolithe has been conclusively 
disproved by ClaparedeJ Claus, Hicks, and others. 

Graber thought If that he had discovered an organ 
of hearing containing an otolithe in the antennae of 
certain Diptera. Mayer,** however, has since examined 

* Transactions of the Entomological Society of London, vol. ii. 

t " De Fabrica et usu anteimarum in Iusectis." 1847. 

X " Beob. iiber den feineren Bau der Fiihk rfachur der Lamelli- 
cornier." 1848. 

§ "Mem. sur l'appareil anditif des Insectes," Ann. Set. Nat , 1858. 

|| "Sur les pretendus organes auditifs des Antennes ehez lea 
Cole'op teres," Ann. Sci. Nat. 9 1858. 

^ " Ueber neue otocystenartige Sinnesorgane der Insekten," Arch, 
fur Mic. Anat, 1879. 

** "Sopra certi organi di Sense- nelle Anteime dei Ditteri," Iteale 
Ace. dei Lincei, 1878-79. 



OLFACTORY ORGANS OF FLY. 



53 



them, and it Appears to be really a sac lined with sense- 
hairs. 

Hicks* described the structure of the antennae in a 




Fig. 40. — Antenna of blowfly (after Hicks), a, Enlarged third segment, showing 
pits ; c, base of the antenna. 



considerable number of insects. On the antenna of the 
blowfly (Musca ; Fig. 40) he found no less than 17,000 
perforations, each leading into a small sac, besides which 

* Transactions of the Linnean Society, 1857-1859. 



54 



ANTENNA OF ICHNEUMON. 



there are larger orifices leading into more complex de- 
pressions, apparently arising from the confluence of a 
number of the simple sacs. At the base of these large sacs 
are a number of papillae, or small hairs. In the dragon- 
fly, each segment of the antenna contains a large con- 
voluted sac. The sacs, in fact, vary much in number, 
size, and form, but Hicks considered that "they all 
possess the same elements, and are formed on the same 
principle." In many cases he traced a nerve to the 

base of the pits. He considered 
that they were generally, if not 
always, closed in by a deli- 
cate membrane, which, indeed, 
sometimes projected in a 
hemispherical, conical, or even 
hair-like form. 

The minute structure of the 
pits was further studied by 
Leydig in 1860. He describes 
them as parts of the integument 
in which the chitine is very 
thin, and more or less depressed, 
centre. This hair may be even 




Fig. 41.— One segmeDt of the an- 
tenna of an Ichneumon (after 
Hicks). 



with a hair in the 
reduced to a mere ring. 

Hicks also called attention to a remarkable speciality 
in the antennae of the Ichneumons, the true nature of 
which he did not, however, correctly ascertain. He 
describes the appearance presented as that of a great 
number of narrow inverted canoes, with a keel-like 
ridge, and each inverted over an oval perforation. He 
regarded these as consisting of a thin transparent 
membrane. Subsequent observations, however, have 
shown that each supposed canoe-shaped membrane is, 



OLFACTORY ORGANS OF WASP. 



55 



in fact, a fine hair, inverted over one of the usual 
pits. 

In 1880 Hauser published an excellent memoir* 
on the olfactory organs of insects, from which I have 
taken Fig. 42, representing a section through part 




IS^m I V=j 





y &jr jp 



Fig. 42.— Section througn part of the antenna of a wasp (after Hauser), x 430. 
CH, Chitinous skin ; Z, olfactory cone ; G, olfactory pit ; TB, tactile hairs ; H, 
hypodermic cells ; M, the membrane surrounding them ; K, nuclei of the olfac- 
tory cells; K t , remains of the earlier upper nucleus ; SK, lower circle of rods ; 
RS, olfactory rod ; GZ, Geisselzelle ; MZ, membrane forming cell ; M, membrane 
closing the pit. 

of the antenna of a wasp, showing two of the 
olfactory cones, one projecting beyond the general 
surface. They terminate above in a fine rod, below in 
a nerve-thread, and present a double series of ridges. 



* "Phys. und Hist. Unt. u. die Geruchsorgane der Insekten," Ztit. 
fur Wiss. Zool, 1880. 



56 



ANTENNAL ORGANS OF INSECTS. 



Kraepelin* and Sazepinf have also published valuable 
memoirs containing many interesting details. 

The hairs of the antennae, then, serve some for touch 
and some for smell, while there is, as we shall presently 
see, strong reason for supposing that the sense of 
hearing is also in some insects seated in the antennae. 

The greatest variety of antennal organs, so far as we 
yet know, occurs in the Hymenoptera (ants, bees, and 
wasps). Of these I give a diagrammatic figure. 
There are at least nine different structures. 

1. Ordinary hairs (Fig. 43, c). 




Fig. 43. — Diagram showing structures on the terminal segments of the antenna of 
insects, a, Chitinous cuticle; b, hypodermic layer; c, ordinary hair; d, tactile 
hair ; e, cone ; /, depressed hair, lying over g, cup, with rudimentary hair at the 
base ; h, simple cup ; i, champagne-cork-like organ of Forel ; k, flask-like organ ; 
I, papilla, with a rudimentary hair at the apex. 



2. Hairs of touch (Fig. 43, d). 



* " Phys. tind Hist. Uiit. ii. die Geruchsorgane der Insekten," Zeit. 
fur Wiss. Zool., 1880 ; and " Ueber die Geruchsorgane der Glieder- 
thiere," 1883. 

t " Ueber den histol. Bau und die Vert, der nervosen Endorgane 
auf den Fuhlern der Myriopoden," Mem. de V 'Acad. Imper. de Sc. de 
St. Petersburg, 1885. 



ANTENXAL ORGANS OF INSECTS. 57 

3. Flattened hairs (Fig. 43, e). 

4. Depressed hairs (Fig. 43, /). 

5. Pits with a minute hair at the base (Fig. 43, g). 

6. Pits without a hair at the base (Fig. 43, h). 

7. Cones containing a nerve (Fig. 43, Z). 

8. The eharnpagne-cork-like organs of Forel (Fig. 
43, i). These consist of a pit, with a constriction about 
halfway up. They differ, in fact, from the second 
sort mainly in the presence of this constriction. 

9. The curious flasks (Fig. 43, h) first observed 
and described by Hicks.* u They consist," he says, " of 
a small pit leading to a long delicate tube, which, 
bending towards the base, dilates into an elongated 
sac having its end inverted." f Of these remarkable 
organs there are about twelve in the terminal segment, 
and one or rarely two in the others. Similar structures 
have since been found in other Hymenoptera ; but not, 
I believe, as yet in any other order of insects. I have 
ventured to suggest that they may serve as microscopic 
stethoscopes. Kraepelin was disposed to regard them 
as glands, but I agree with Forei that there is no suffi- 
cient reason for doinp: so. 

There may, moreover, be a distinctly characterized 
sense-organ without any alteration of the actual 
surface, as shown in some of the figures oiven by 
Kraepelin, and also by that from Hauser given above 
(Fig. 42). 

These are, perhaps, the principal types, but there 

* Transactions of the Linnean Society, vol. xxii. p. 39. Kraepelin 
attributes the observation to Forel, but this is an error. Forel had 
overlooked Hicks's description and figure. 

f Hicks, " On the Organs of the Antennae of Insects," Transactions 
of the Linnean Society, vol. xxii. 



58 COMPLEX STRUCTURE OF THE ANTENNA. 

are many modifications ; for instance, complex pits 
often arise from the confluence of several small ones. 
The structure of the antennae is then very complex, and 
increases with the importance of the antennae in the 
life of the insect. Among the Hymenoptera, Lyda has 
about 600 pits; Tenthredo, 1200; Sirex, 2000; Pompilus, 
3000; Paniscus, 4000; Ichneumon, 5000; Hyloeus, 
6000; the wasp (Vespa), about 13,000 pits and 700 
cones ; the blowfly, 17,000 ; the hive bee, according to 
Hicks, about 20,000 pits and 200 cones. Among beetles 
(Coleoptera) the numbers are generally small, but the 
cockchafer (Melolontha) possesses, according to Hauser, 
on each antenna as many as 35,000 in the female, and 
39,000 in the male. Moreover, it is significant that in 
those species where the females are quiescent and are 
actively sought out by the males, the antennae are 
much less highly developed in the female sex than in 
the male. 

As already mentioned, the antennae probably serve 
partly as organs of touch, and in some cases for smell. 

On the other hand, I do not believe that touch and 
smell are the only two senses possessed by the antennae. 
Forel and I have shown that in the bee the sense of 
smell is by no means very highly devel ped. Yet 
their antenna is one of those most highly organized. 
It possesses, as I have just mentioned, besides 200 
cones, which may probably serve for smell, as many as 
20,000 pits ; and it would certainly seem unlikely 
that an organization so exceptionally rich should solely 
serve for a sense so slightly developed. 

Much as these antennal structures differ from one 
another in form, arrangement, and structure, they are 
all reducible to one type — to a hair — more or less de- 



VARIOUS USES OF ANTENNA. 59 

veloped, more or less deeply seated, standing in con- 
nection with the ganglionic cells, and so with the cerebral 
ganglia. Even the long-necked " bottles " (Fig. 43, h) 
may be regarded as an extreme form of this type, 
especially if the inversion at the end can be, as seems 
probable, regarded as a hair. 

All entomologists are agreed that some of the anten- 
nal hairs serve as organs of protection, and others as 
organs of touch. The evidence is, as we have seen, very 
strong, that some of them serve as organs of smell. 
They fulfil, therefore, at least three different functions, 
and when we consider their manifold variety, there is 
not only no a priori improbability, but, on the contrary 
it seems very probable that some of them, at least, 
perform some other function in the animal economy. 

There is, indeed, strong reason, as we shall see in the 
next chapter, to believe that, in some cases at any rate, 
the antennae act also as ears ; while some of these 
peculiar antennal organs, though obviously organs of 
sense, seem to have no special adaptation to any sense 
of which we are cognisant. 



CHAPTEE IV. 

THE SENSE OF HEAEING. 

The sensation of sound is due to vibrations of the air 
striking on the drum of our ear. The intensity of the 
sound depends on the extent or amplitude of the sound- 
wave; while the pitch of the tone depends on the fre- 
quence of vibration, and consequently on the number of 
waves which strike the ear during a given interval. 
The fewer the number of vibrations in a second, the 
deeper the sou Lid ; the more numerous, the shriller it 
becomes. Our pianos generally begin with the C of 
32 vibrations in a second, and extend to A"" of 3520 
vibrations. The number of vibrations for the tone 
A', which is that of the hum of a bee, is about 440 
in a second. If the vibrations are fewer than 30 in a 
second, they produce only a buzzing and groaning 
sound, while the shrillest sound we can hear is produced 
by about 35,000 vibrations in a second. 

It may seem curious that there should be any dif- 
ficulty in ascertaining whether an animal can hear. 
But, in the first place, in order to experiment on 
them, we are often obliged to place them in situa- 
tions very unlike those to which they are accustomed ; 
and, secondly, it is by no means always easy to say 



ORGANS OF SOUND — MOLLUSCA — CRUSTACEA. 61 

whether they are affected by a real noise, or whether 
they are merely conscious of a concussion or vibration. 

As regards the lower animals, it appears to me, I con- 
fess, that many organs have been described as auditory, 
on grounds which are anything but satisfactory. At 
the same time, it cannot be doubted that many of the 
lower animals do possess the power of hearing, especially 
as some have elaborate organs for the production of 
sound. 

Among the lowest groups, none of the Protozoa or 
Coelenterata are known to produce sounds, and in the 
Mollusca, also, the power is very rare. The Pectens, 
which are the most lively of bivalves, moving actively 
by the sudden opening and closing of their valves — as 
Pliny says, " Saliunt Pectines et extra volitant seque 
ipsi carinant" — also produce in the same way a certain 
sound, which Aristotle* gives as an exceptionalease 
among the Mollusca. 

Nor is the production of sound much more frequent 
among the Crustacea. In one genus of crahs (Ocypoda), 
the claw bears a rasp, or file, which can be rubbed against 
a ridge on the basal segment of the limb, and thus 
produces a harsh, jarring sound. Some of the lobsters 
also (Palinurus) make a noise by rubbing one segment 
of the antennae against another ; but, considering that 
the ear is w 7 ell developed in this group, it is rather 
remarkable how few of them are known to possess the 
power of producing sounds. 

Passing on to the insects, the song of the Cicada has 
been celebrated from time immemorial ; the chirping of 
the crickets and grasshoppers is also familiar to us all. 

For the reasons, however, already alluded to in the 

* " Historia Animalinm." 



62 INSECTS— LOCUSTS. 

preceding chapter, no insect possesses a true voice. The 
sounds they make are produced in various ways — for 
instance, by the wings or the spiracles, by rubbing one 
part of the body against another, etc. 

The power of producing sounds audible to us is pos- 
sessed by many insects scattered sporadically through 
all the great groups. 

In many of these cases, the power of producing sound 
is confined to the males. Their sounds are really love- 
songs.* 

In Locusts, as Westwood says,f "The stridulating 
powers of these insects must have attracted the notice 
of every one who has walked through the fields in the 
autumn. Unlike the insects of the two preceding 

families, it is owing to the motion 
of the hind femora, either con- 
jointly or alternately rubbed 
against the sides of the wing- 
covers, that the sound is pro- 
duced, the insects resting on their 
four anterior legs during the 
operation ; the veins of the wing- 
Fig. 44.— Leg of stenobothms covers being considerably ele- 

pratorum (after Landois). ° J 

vated, so as to be easily acted 
upon by the rugose inner edge of the thigh. Some 
species, according to Goreau, may be observed to exe- 
cute this movement without producing any sound per- 
ceptible to our ears, but w r hich he thinks may be per- 
ceived by their companions." 

* The females are not, however, invariably dumb. In Ephippigera 
both sexes are able to produce a sound, which, however, is not very 
loud. 

t Westwood, " Modern Classification of Insects." 




GRASSHOPPERS— CRICKETS. 63 

Fig. 44 represents the leg of a grasshopper (Steno- 
bothrus pratorum). On the inner side of the thigh, at 
s, is a file, consisting of a row of fine teeth (Fig. 45, z), 
which rub against the wing-covers, and thus produce the 
well-known sounds. 

Lehmann states that Brunelli " kept and fed several 
males of G-ryllus viridissimus in a closet, which were 
very merry, and continued singing all the day; but a 
rap at the door would stop them instantly. By practice 
he learned to imitate their chirping ; when he did this 
at the door, at first a few would answer him in a low 
note, and then the whole party would take up the tune 
and sing with all their might. He once shut up a male 
of the species in his garden, and gave a female her 
liberty ; but when she 

heard the male chirp, £k /t% Jk $S J&k lKJh_Jkr~* / 
she flew to him im- 
mediately." * 

In the males of 
the house and field 
crickets, the source of * 

tlio cm-mrl ic rliffavpnt Fig. 45.— Sound-bow of Stenobothrus (after 

me hUUUQ lb Uineieni. Landois). s, Surface of the skin ; z, teeth. 

On the inner margin 

of the left wing-cover, about one-third of its length 
from the base, a thickened point is observed, from 
which several strong veins diverge. The strongest of 
these veins, that running towards the base of the wing- 
cover, is regularly notched on the under side trans- 
versely, like a file. When the wing-covers are closed, 
this oblique bar of the wing-cover lies upon the upper 
surface of the corresponding part of the right wing- 

* " De Sensibus externis Animalium exsangiiinium." Gottingen : 
1798. I give Kirby and Spence's translation. 
5 




64 CICADAS— BEETLES. 

cover, and when a tremulous motion is imparted to the 
wing-covers, this bar rubs against the corresponding 
bar of the right wing-cover, and thus produces the 
familiar chirping sound. 

The song of the Cicadas is produced, again, in a dif- 
ferent manner. The musical organs are internal, are 
placed " at the base of the abdomen beneath, and are 
covered by two large flat plates attached behind the 
place of insertion of the hind legs, varying in form in 
the different species, being, in fact, the dilated sides 
of the metasternum. . . . The sound issues out of two 
holes beneath the above-mentioned plates, in a manner 
somewhat analogous to the action of a violin."* 

Many beetles have special organs for the production of 
sounds. A remarkable case is that of the so-called 
" bombardier beetles," which, when attacked, discharge 
at the enemy, from the hinder part of their body, an 
acrid fluid which, as soon as it comes in contact with 
air, explodes with a sound resembling a miniature gun. 
Westwood mentions, on the authority of Burchell, that 
on one occasion, " whilst resting for the night on the 
banks of one of the large South American rivers, he 
went out with a lantern to make an astronomical ob- 
servation, accompanied by one of his black servant 
boys ; and as they were proceeding, their attention was 
directed to numerous beetles running about upon the 
shore, which, when captured, proved to be specimens 
of a large species of Brachinus. On being seized, they 
immediately began to play off their artillery, burning 
and staining the flesh to such a degree that only a few 
specimens could be captured withthenaked hand, leaving 
a mark which remained a considerable time. Upon ob- 

* Westwood, "Modern Classification of Insects," vol. ii. p. 42. 



THE BOMBARDIER BEETLE — PAUSSUS. 65 

serving the whitish vapour with which the explosions 
were accompanied, the negro exclaimed in his broken 
English, with evident surprise, 'Ah, massa, they make 
smoke ! ' " * 

A similar means of defence is possessed by beetles 
belonging to a very different family — the Paussidae. 
Captain Boyes mentions f that on one occasion, having 
captured a Paussus Fichtelii " it immediately emitted 
two loud and very distinct crepitations, accompanied 
with a sensation of heat, and attended by a strong 
acidulous scent. It left a dark-coloured stain on the 
fingers resembling that produced by caustic, and 
which had a strong odour something like nitric 
acid. A circumstance so remarkable induced, me to 
determine its truth, for which purpose I kept it alive 
till the next morning, and, in order to certify myself of 
the fact, the following experiments were resorted to. 
Having prepared some test-paper by colouring it with 
a few petals of a deep red oleander, I gently turned 
the Paussus over it, and immediately placed my finger 
on the insect, at which time I distinctly heard a crepi- 
tation, which was repeated in a few seconds on the 
pressure being renewed, and each discharge was ac- 
companied by a vapour-like steam, which was emitted 
to the distance of half an inch, and attended by a very 
strong and penetrating odour of nitric acid." 

I do not, however, refer to these cases as affording 
any evidence that the insects themselves possess the 
power of hearing, but merely on account of their 

* Westwood, " Modern Classification of Insects," vol. i. p. 76. ■ 
t " The Economy of the Paussidae," Ann. and Magazine of Natural 
History, vol. xviii. ; see also Peringtiay's "Xotes on Three Paussi," 
Transactions of the Entomological Society, 1883, p. 133. 



66 DEATH-WATCH — BURYING BEETLES. 

intrinsic interest. The following instances, however, 
do seem to imply a pow T er of hearing. 

A well-known case is that of the death-watch, 
associated with so many superstitions, and supposed 
in old days to be a certain indication of approaching 
death. In this case the insect produces the sound by 
tapping with its head or abdomen, or, according to 
Doubleday, with its thorax. If a male death-watch 
ticks, and there be a female even within several yards, 
she returns the tap, and they approach one another 
slowly, tapping at intervals, until they meet. The 
male Ateuches stridulates to encourage the female in 
her work, and also, according to Darwin, " from distress 
when she is removed." * 

It has long been known that among the Longicorn 
beetles many of the species, when alarmed, " produce 
a slight but acute sound by the friction of the narrowed 
anterior part of the mesothorax, or rather a polished 
part of the scutellum, against the edge of the protho- 
racic cavity, by w r hich motion the head is alternately 
elevated and depressed. It has been generally stated 
that it was by the friction of the hind margin of the 
thorax against the base of the elytra that this sound 
was produced, but this is not the case."t The burying 
beetles (Necrophorus) produce a sound by rubbing the 
abdomen against the hinder edges of the wing-cases. 

Wollaston, in a short paper on certain musical 
Curculionid8e,f describes a species of Acalles, which he 
found in Teneriffe. A number of specimens were in a 
hollow stem, and when it was shaken "the whole plant 

* "Descent of Man," vol. i. 

t Westwood, " Modern Classification of Insects," vol. i. 

J Ann. and Magazine of Natural History, 1860. 



WEEVILS— COCKCHAFERS. 67 

appeared musical." In this genus the sound is produced 
by rubbing the tip of the abdomen, so rapidly that the 
movements were scarcely visible to the eye, against the 
under surface of the ends of the elytra, or wing-cases. 
The tip of the abdomen, though roughened, is not con- 
spicuously so, the ends of the elytra are shagreenecl, 
though very finely, and Wollaston expresses his surprise 
that so small an instrument could produce so loud a 
noise. He describes a similar structure in other species 
of the group. 

The cockchafers (Melolontha), besides the humming 
of the wings, produce a sound which may almost be 
called a voice. In the large trachea, immediately 
behind each spiracle, is a chitinous process, or tongue, 
which is thrown into vibration by the air during respi- 
ration, and thus produces a humming noise. 

In the beetles, then, the sounds produced may be 
divided into three classes : 

1. Incidental, such as those produced during 
flight. 

2. Defensive. 

3. For signals, as in Longicorn beetles, Ateuches, 
Anobium, etc. 

Laudois gives the following summary of the different 
modes in which sounds are produced by the Cole- 
optera : — 

1. Tapping sounds (Bostrychidse, Anobium). 

2. Grating sounds (Elaterida). 

3. Friction without rasping organs (Eucliirus Ion- 
gimanus). 

4. Easping sounds produced by friction, viz. — 

(1) Pronotum on Mesonotum (Cerambycida, with 
the exception of Sponclylis and Prionus). 



68 VARIETY OF ORGANS OF SOUND AMONG BEETLES. 

(2) Prosternum on Mesosternura (Omaloplia 

brunnea). 

(3) Elytra with rasp at the end (Curculionida ; 

Dytiscida, Pelobius). 

(4) Coxae with rasp (Geotrupes, Ceratophyus). 

(5) Cover-margin rasp rubbing against the thigh 

{Ghiasognathus Orantii). 

(6) Pygidium with two rasps in the middle 

(Crioeeris, Lerna, Copris, Oryctes, Necro- 
phorus, Tenebrionida). 

(7) Abdomen with a grating-ridge and four 

grating-plates (Trox sabulosus). 

(8) Abdomen with two toothed ridges rubbing 

on cover-margin rasp (Elaphrus, Blethisa, 
Cychrus). 

(9) Elytra rubbing with under-wing rasp {Pelobius 

Eerrmanni). 

(10) Wings rubbing against abdominal ringlets 
(Melolontha fullo) . 

5. Exploding sounds from the tail (Brachinus). 

6. Sounds produced by the spiracles (Melolontha). 
Graber, moreover, has shown by a number of 

interesting experiments * that the power of hearing is 
by no means confined to those beetles which are known 
to produce sounds themselves. 

Passing on to other groups of insects, flies and gnats, 
besides the humming of the wings, produce sounds, 
like the cockchafer, through the spiracles, some of 
which are especially arranged for this purpose. If a 
fly be caught and held between the fingers, it will 
generally make a loud and peculiar sound. The hum 
of the mosquito is only too familiar to most of us. 

* "Die Ckordotonal Sinnesorgane der Insekteu," Arch, fur Mic. 
Anat, 1882. 



DIPTERA — HYMENOPTERA. 69 

Landois mentions that he has heard species of 
Eristalis and Syrphus sing while they have been 
sitting quietly. The dragon-flies (Libellulina) also 
produce a sound by means of their spiracles. 

Among Hymenoptera, the hum of an angry bee is 
proverbial. Nor must I omit to mention the piping 
noise made by young queen bees. It is well known 
that there is only one queen in a hive, and that 
working bees never turn their back on her; as she 
moves among the combs, they all turn towards her. 
If there has been a swarm led by the old queen, the 
young queen who has succeeded often makes a piping 
noise, first noticed by Huber, whose statements are 
generally recognized as correct.* While "singing" 
the queen assumes a particular attitude, and the other 
bees all lower their heads and remain motionless until 
she begins to move again. In the mean while, if there 
are any other young queens which have not yet left 
the cells, they answer the old one, and their notes seem 
to be sounds of challenge and defiance. 

Other bees. also produce a sound by means of their 
spiracles quite different from the humming of their 
wings. Mutilla Europsea, a wingless species, related to 
and not unlike the ants, makes, when alarmed, a rather 
sharp noise by rubbing one of the abdominal rings 
against the other. 

Under these circumstances, Landois asked himself 
whether other genera allied to Mutilla might not 
possess a similar organ, and also have the power of 
producing sound. He first examined the genus Ponera, 
which, in the structure of its abdomen, nearly resembles 

* Huber, M Obs. sur les Abeilles; " Bevan, " On the Honey Bee ;" 
Langstroth, " On the Honey Bee." 



70 ANTS — BEES. 

Mutilla, and here also he found a fully developed 
stridulating apparatus. 

He then turned to the true ants, and here also he 
found a similar rasp-like organ in the same situation. It 
is indeed true that ants produce no sounds which are 
audible by us ; still, when we find that certain allied 
insects do produce sounds appreciable to us by rubbing 
the abdominal segments one over the other, and when 
we find, in smaller species, an entirely similar structure, 
it certainly seems reasonable to conclude that these 
latter also do produce sounds, even though we cannot 
hear them. Landois describes the structure in the 
workers of Lasius fuliginosus as having twenty ribs in 
a breadth of *13 of a millimeter. In Lasius flavus I 
found about ten well-marked ribs, occupying a length 
of iJq- of an inch. Similar ridges also occur between 
the following segments. 

In the flies (Diptera) and dragon-flies (Libellulina), 
the four thoracic spiracles produce sounds ; while in- 
Hvmenoptera, as, for instance, in the humble bee 
(Bombus), the abdominal spiracles are also musical. 
The sounds produced by the wings are constant in 
each species, excepting where there are (as in Bombus) 
individuals of very different sizes. In these the 
larger specimens give generally a higher note. Thus 
the comparatively small male of Bombus terrestris 
hums on A', while the large female hums a whole 
octave higher. There are, however, small species 
which give a deeper note than larger ones, on account 
of the wing-vibrations not being of the same number 
in a given time. Moreover, a tired insect produces a 
somewhat different note from one that is fresh, on 
account of the vibrations being slower. 



SOUNDS PRODUCED IN FLIGHT. 71 

Indeed, from the note produced we can calculate the 
rapidity of the vibration. The slow flapping of a 
butterfly's wing produces no sound, but when the move- 
ments are rapid a noise is produced, which increases 
in shrillness with the number of vibrations. Thus the 
house-fly, which produces the sound of F, vibrates its 
wings 21,120 times in a minute, or 335 times in a 
second ; and the bee, which makes a sound of A', as 
many as 26,400 times, or 440 times in a second. On 
the contrary, a tired bee hums on E', and therefore, 
according to theory, vibrates its wings only 330 times 
in a second. 

Marey has succeeded in confirming these numbers 
graphically. He fixed a fly so that the tip of the 
wing just touched a cylinder which was moved by 
clockwork. Each stroke of the wing caused a mark, 
of course very slight, but still quite perceptible, and 
he thus showed that there were actually 330 strokes in 
a second, agreeing almost exactly with the number 
inferred from the note produced. 

The sound emitted from the spiracles bears no re- 
lation to that produced by the wings. Thus, according 
to Landois, the wing-tone of the hive bee is A' ; its 
" voice," if we may call it so, on the contrary, is an 
octave higher, and often goes to B" and C". In one of 
the solitary bees, Anihidium manicatum, the difference 
is still greater ; the wing-tone is G-', and the " voice " 
nearly two octaves higher, reaching to F ; ". 

The wing-tone is constant, at least with the excep- 
tions just alluded to. The " voice," on the contrary, 
appears to be to some extent under the control of the 
will, and thus offers another point of similarity to a true 
" voice." Thus a bee in the pursuit of honey hums 



72 POWER OF VARYING SOUND. 

continually and contentedly on A', but if it is excited 
or angry it produces a very different note. Thus, 
then, the sounds of insects do not merely serve to bring 
the sexes together ; they are not merely " love-songs," 
but also probably serve, like any true language, to 
express the feelings. 

Landois also describes the muscles by means of 
which the form of the organ, the tension of the drum, 
etc., is altered, and the tone thus, no doubt voluntarily, 
affected.* We can, indeed, only in few cases distinguish 
the differences thus produced; but as even we, far 
removed as we are in organization, habits, and senti- 
ments, from a fly or a bee, can yet feel the difference 
between a contented hum and an angry buzz, it is highly 
improbable that their power of expressing their feelings 
should stop there. One can scarcely doubt but that 
they have thus the means of conveying other sentiments 
and ideas to one another. 

Butterflies and moths do not habitually produce any 
sound in flight. The texture of their wings is com- 
paratively soft, and they are generally moved slowly. 
Still, they are not altogether silent. 

The death's-head moth {Sphinx atropos) emits a 
mournful cry, first noticed by Reaumur. This moth, 
he says, " dans le temps qu'il marche, a un cri qui a 
paru funebre ; au moins est-il le cri d'une bonne ame 
de papillon, s'il gemit des malheurs qu'il annonce. 

"Le cri de notre papillon est asses fort et aigu; il a 
quelque ressemblance avec celui des souris, mais il est 
plus plaintif ; il a quelque chose de plus lamentable. 
C'est surtout lorsque le papillon marche, ou qu'il se 

* " Die Ton and Stiiiim Apparate der Insektcn," Zeit. fiir Wiss 
Zool, 1866. 



BUTTEEFLIES— MOTHS. 73 

trouve mal a son aise, qu'il crie ; il crie dans les poudries, 
dans les boistes ou on le tient renferme ; ses cris 
redoublent lorsqu'on le prencl, et il ne cesse de crier 
tant qu'on le tient entre les doigts. En general il fait 
grand usage de la faculte de crier, que la nature lui a 
accordee." * 

There has been much doubt how the sound arises, but 
it appears to be ascertained that the moth produces it 
by rubbing the palpi against the base of the proboscis.! 

Huber thought, and subsequent writers — as, for 
instance, Kirby and Spence, and Bevan — have con- 
curred in the opinion, that the sound "operates on the 
bees like the voice of their queen, and thus enables 
the moth to commit the greatest ravages in the hives 
with perfect immunity." J On the other hand, Huber 
ascertained by experiment that it exercises no such 
charm over humble bees. 

Several other species of the genus Sphinx also pro- 
duce a sound, and a few other moths, for instance, 
Noctua fovea. Darwin also mentions § a Brazilian 
butterfly, Ageronia feronia, as making " a noise like 
that produced by a toothed wheel passing under a 
spring catch, which could be heard at the distance 
of several yards." 

The peacock butterfly (Vanessa io) || is also said to 
possess the same power. 

For further details with reference to the sounds 
produced by insects, and, indeed, by animals generally. 

* " Mem. p. servir a l'Histoire des Insectes." 

t Landois, " Die Ton und Stiinm Apparate der Insekten," Zeit. fiir 
Wus. Zool. 9 vol. xvii. 

X Bevan, " On the Honey Bee." § " Descent of Man," vol. i. 

|| " Die Ton and Stimin Apparate der Insekten," Zeit fur Wiss. 
Zool, 1867. 



74 CENTIPEDES— SPIDEKS. 

I may refer to Landois's interesting work, "Thier- 
stimmen." 

From the fact that the power of producing sounds 
audible to us is scattered among so many groups, and 
that the sounds themselves are often so shrill, I am 
disposed to suspect that many insects usually regarded 
as dumb really produce sounds, which, however, are 
beyond our range of hearing. 

Among centipedes Gerstacker has described* a 
sound-producing organ in Eucorybar crotylus. The 
posterior legs have the fourth segment much enlarged 
and leaf-like, with the edges raised and formed of 
very hard chitine. The legs are rubbed against one 
another, and thus produce a rasping sound. Bourne 
also has recently described t a stridulating organ in 
another genus (Sphserotherium). It is situated just 
behind the twenty-first pair of legs, and consists of a 
hood-like process bearing a number of parallel ridges. 

There is a very general impression that spiders hear 
well, and even enjoy music ! There seems, however, 
very little evidence of any value on the subject. No 
doubt they are extremely sensitive to vibrations. The 
presence of even a very small insect on their web is 
at once perceived. Mr. Boys has shown that the 
vibrations of a tuning-fork affect them strongly.J 
This sensitiveness to vibrations is, however, not neces- 
sarily the same as a true sense of hearing. Kraepelin 
says § that he knows only one observation which seems 
to him to possess sufficient exactness to justify the 
conclusion that spiders possess any sense of hearing — 
namely, that of Lehmann. 

* Gerstacker, " Stettin Ent. ZeiL, 1854. 

t Bourne, Linnean Journal, 1885. X Nature, vol. xxiii. 

§ " Ueber die Geruchsorgane der Gliederthiere." 



POWER OF HEARING IN INSECTS. 75 



It would be, on the other hand, most unsafe to 
conclude that spiders are incapable of hearing. Dahl * 
has given reasons for believing that some of their hairs 
serve as auditory organs. Westring has discovered, 
in certain species of Theridium (T. serratipes, ocidatum, 
castaneum, etc.), a stridulating organ, consisting of a 
sort of raised bow attached to the upper part of the 
abdomen, which rubs against the under and hinder 
part of the cephalothorax, producing a whirring sound. 
Lebert t naturally observes that this appears to indicate 
a power of hearing on their part. 

As regards insects, it would be easy to multiply such 
evidence almost indefinitely ; I have given more illus- 
trations than I should probably have otherwise thought 
necessary, because so excellent an observer as Forel, 
whose opinion I should value on such a point as much as 
that of any authority, expresses doubt whether insects 
really hear at all. " Ce qu'on semble," he says, in his 
last memoir on the subject, " considerer comme preuve 
de 1'ouie me parait comme a Duges reposer a peu d'excep- 
tions pres sur des ebranlements mecaniques de Fair ou 
du sol qui sont simplement percus comme tels par les 
organes tactiles des insectes. Cela correspond a peu 
pres a la derniere opinion de Graber sur " 1'ouie " de 
la Periplaneta. Mais on n'a pas le droit de nommer 
ouie de pareilles sensations." i. 

Graber, however, has endeavoured to meet this 
objection by an ingenious experiment^ He placed 
some water-boatmen (Corixa) in a deep jar full of 

* " Das Gehor-und Gerucbsorgane der Spiimen," Arch, fur Mic. 
Anat, 1885. 

f " Die Spiimen der Schweiz." 

X A. Forel, " Sensations des Insectes," Becueil Zool. Suisse, t. iv. 1887. 

§ Arch, fur Mic. Anat, 1882. 



76 SENSE OF HEAEING IN INSECTS. 

water, at the bottom of which was a layer of mud. 
He dropped a stone on the mud, but the beetles, 
which were reposing quietly on some weeds, took no 
notice. He then put a piece of glass on the mud, 
and dropped the stone on to it, thus making a noise, 
though the disturbance of the water was the same. 
The water-boatmen, however, then at once took flight. 
In face of all the evidence, then, I do not think 
there can reasonably be any doubt on the subject, and 
it seems to be clearly established that insects do possess 
the sense of hearing. 



CHAPTER Y. 

THE OKGASTS OF HEATJNG. 

That many of the lower animals have special organs 
for the production of sound, and possess the sense of 
hearing, has been shown in the preceding chapter. 

I now proceed to consider the mechanism by which 
sounds are perceived. In our own ear we have, first 
of all, the external ear, much less important in man 
than in many other animals, as in the horse, for 
instance, where it may be seen moving continually, and 
almost automatically assuming the position most favour- 
able for conveying the waves of sound down the outer 
passage (Fig. 46, D) to the tympanum, or drum. This is 
a membrane stretched between the outer air on the one 
hand, and the drum on the other, which also contains 
air, transmitted through the mouth by means of the 
Eustachian tube (Fig. 46, E). The drum is separated 
from the brain by a hard, bony partition in which are 
two orifices, one oval and the other round. Across the 
drum stretches a chain of little bones (Fig. 47) ; first 
the "hammer," secondly the "anvil," and lastly the 
" stirrup." The flat plate of the stirrup, again, lies 
against the oval orifice, or fenestra ovalis, as it is techni- 
cally called, of the drum. Thus the sounds are intensi- 



78 



STRUCTURE OF THE HUMAN EAR. 



fled by being conveyed from the tympanic membrane 
to one which is twenty times smaller. Behind the 




Fig. 46.— Diagram of human ear (after Bernstein). D, Auditory canal; E, mouth of 
Eustachian tube ; cc, tympanic membrane ; B, tympanic cavity ; o, fenestra ovalis ; 
r, fenestra rotunda ; s, semicircular canals ; A, cochlea. 

fenestra ovalis is the labyrinth, which is filled with fluid, 

and on which the final 



Am. 



Am. k 



filaments of the auditory 
nerve are distributed. 
This fluid is thrown into 
vibrations by those of the 
stirrup, but as it is en- 
closed in a bony case, the 
vibrations would be great! y 
curtailed if it were not for 
the second membrane, or 
fenestra rotunda. This 
round membrane, there- 
fore, acts as a counter 
opening, for if the fluid is 
compressed in one place, it must claim more room in 
another. The labyrinth consists mainly of two parts, 




Fig. 47. — Ossicles of the ear. H, Hammer ; 
Am, anvil ; Am. k, shorter process of the 
anvil; Am. I, longer process of the anvil; 
S, stirrup ; St, long process of the 
hammer. 



STRUCTURE OF THE HUMAN EAR. 



79 



z 



the cochlea and the semicircular canals. The semi- 
circular canals are three in number, and stand at right 
angles to one another. No satisfactory explanation of 
their function has yet been given ; but there is some 
evidence that, in addition to, or apart from, hearing, 
they are affected by the position of the head, and thus 
serve as organs for maintaining the equilibrium of the 
body. Each of the canals commences with an oval 
dilatation, or ampulla. 
In the ampulla is a 
projecting ridge, on 
which are long, stiff, 
delicate, hair-like pro- 
cesses, the vibrations 
of which probably give 
certain sound-sensa- 
tions. In the canals 
certain parts bear 
shorter hairs, over 
which are minute ear- 
stones, or otolithe*, 
consisting of carbonate 
of lime, embedded in 
a gelatinous substance. 
The cochlea contains, 
moreover, a compli- 
cated and wonderful organ, discovered by Count Corti. 
This appears to be, in fact, a microscopic musical instru- 
ment, composed of some four thousand complex arches, 
increasing regularly in length and diminishing in 
height from the base to the summit of the cochlea. 
The waves of sound have been supposed to play on 
this organ, almost like the fingers of a performer on 
the kevs of a musical instrument. 




J\T 



Fig. 48. — Section through the ampulla (after 
Bernstein). N, Kerve ; z, terminal cells; h, 
auditory hairs. 



80 



THE ORGAN OF CORTI. 




Fig. 49. — Tympanal wall of the ductus cochlearis, from the dog. Surface view from 
the side of the scala vestibuli/ after the removal of Reissner's membrane, 3^0. I. 
Zona denticulata Corti. II. Zona pectinata Todd- Bowman : 1, Habenula sulcata 
Corti ; 2, Habenula denticulata Corti ; 3, Habenula perforata Kolliker. III. Organ 
of Corti : a, portion of the lamina spiralis ossea (the epithelium is wanting) ; b and 
c, periosteal blood-vessels ; d, line of attachment of Keissner's membrane ; e and 
e„ epithelium of the crista spiralis ; /, auditory teeth, with the interdental furrows ; 
g, g n large-celled (swollen) epithelium of the sulcus spiralis internus, over a certain 
extent shining through the auditory teeth ; from the left side of the preparation 
they have been removed ; h, smaller epithelial cells near the inner slope of the 
organ of Corti ; 7c, openings through which the nerves pass ; i, inner hair cells ; 
I, inner pillars ; m, their heads; o, outer pillars; n, their heads; p, lamina 
reticularis ; q, a few mutilated outer hair cells ; r, outer epithelium of the ductus 
cochlearis (Claudius's cells of the author's) ; removed at s in order to show the 
points of attachment of the outer hair cells. After Waldeyer, in Strieker's 
"•Manual of Histology." 



MODE OF ACTION OF AUDITORY ORGANS. 81 

The fibres of Corti, according to Helniholtz, may 
be distributed among the seven octaves which are in 
general use, so that there will be 33J- fibres to every 
semitone, and 400 to each octave. Weber has esti- 
mated that a skilful ear can perceive a difference even 
of the g*£ of a tone, or nearly four thousand sounds, and 
this would agree fairly well with the number of fibres. 

But why, it may be asked, should a given musical 
sound act more on one of these " keys " than another ? 
If several tuning-forks which sound different notes 
are placed on a table, and another in vibration be 
brought near. them, the one sounding the same note is 
thrown into vibration, while the others are unaffected. 
A second tuning-fork would affect its own fellow, but 
no other, and so on.* A very slight change in the 
tuning-fork, such,, for instance, as would be made by 
fastening a piece of wax to one of the prongs, is 
sufficient to destroy the sympathetic vibrations. The 
sound of the human voice has been known to break a 
bell-shaped glass by the agitation thus caused. The 
difficulty is to hit the pitch with sufficient precision, 
and retain the tone long enough. It is probable, 
therefore, that each of Corti's arches is set for a 
particular sound, and sensitive to it alone. This 
suggestion derives additional probability from the 
observations of Hensen (see p. 93) on the auditory 
hairs of Crustacea. 

We thus obtain a glimpse, though but a glimpse, of 
the manner in which the arches of Oorti may possibly 
act. There are many problems still to be solved, but 
it is at least easy to see that so complex an organ may 
be capable of conveying very complex sensations. 

* Helmholtz, " Sensations of Tone." 



82 ORGANS OF HEARING IN THE LOWER ANIMALS. 

On the Organs of Hearing in the Lower 
Animals. 

The semicircular canals in the human ear (see p. 79) 
have been supposed by some, in addition to, or apart 
from, their functions as organs of hearing, to assist in 
maintaining the equilibrium of the body ; at all events, 
when they are injured, the movements frequently be- 
come disorderly, and the otolithic organs of the lower 
animals appear, at any rate in certain cases, to perform 
a similar function.* 

Otolithes, as we have seen, are present in our own 
ears, but they play a much more important part in 
those of the lower animals. In the lowest, the sound- 
waves may be considered to produce a certain effect 
upon the general tissues. The soft parts of the body 
are, however, not well calculated to receive such 
impressions. Their effect would be heightened by the 
presence of any solid structures, whether spicules, as 
in sponges, etc., or solid hairs projecting from the 
general surface, as in a great many of the lower 
animals. 

The Medusae (jelly-fishes, Fig. 50) present round the 
edge of the umbrella certain u marginal bodies," with 
reference to which there have been great differences of 
opinion. O. F. Miiller, by whom they were discovered, 
regarded them as orifices for the exclusion of digested 
food, Eosenthal and Escholtz considered them to be 
glands, Milne Edwards as ovaries ; but it seems now 
clearly established that some are organs of hearing, 

* Delage, " Sur une fonction nouvelle des Otocystes," Arch. d. Zool. 
Exp., 1887. Engelinann, " Ueber d. Function der Otolitnen," Zool 
Anz. t 1887. 



MEDUSA. 



83 




Fig. 50.~Eutima gigas (after Haeckel). 



84 



MEDUSA. 



and others of sight. Some species possess both, but, as 
a general rule, among Medusae, where organs of hearing 
are present, those of sight are wanting, and vice versa. 
It may seem extraordinary that there should be such 
differences of opinion as to these organs. The earlier 
naturalists, however, had but imperfect microscopes, 
and probably often examined specimens in a bad state 
of preparation. As regards the alternative between 
the view that they served as eyes and that which 
regarded them as ears, it must, moreover, be remem- 
bered that as long as we merely know that there was 
a capsule containing a transparent body, the function 
might well be doubtful. 

The auditory organs of the jelly-fishes were first 
recognized as such by Kolliker.* They are ranged 
round the umbrella, and vary considerably in number, 
ranging up to sixty in Cunina, eighty in Mitrocoma, 
and as many as six hundred in (Equorea. 

There are three types. In the first, the auditory 
organ is an open pit, lined with cells. The majority of 
those on the outer side contain an otolith e, while a row 

on the opposite side are strap- 
shaped, their free ends termi- 
nating in auditory hairs, which 
reach to the cells containing 
the otolithes, while their inner 
ends are continuous with fibres 
from the inner nerve-ring. 

In such an auditory organ 
as that of Ontorchis (Fig. 51), 
the otolithes present a very deceptive resemblance to 
the lenses of an eye. 

* "Ueber die Randkorper der Quallen," Frorieps Neue Not, 1843. 




Fig. 51. — Auditory organ of Ontor- 
chis Gegenbauri. 



MEDUSA. 



85 



Fig. 52 represents the somewhat more complex 
auditory organ of Phialidium. 







Fig. 52. — Auditory organ of Phialidium (after Hertwig). cZ 1 , Epithelium of the upper 
surface of the velum ; cP, epithelium of the under surface of the velum ; hh, 
auditory hairs ; h auditory cells ; np, nervous cushion ; nr', nerve-ring ; r, 
circular canal at the edge of the velum. 

The second type is more advanced, the vesicle being 
closed, and the otolith es fewer in number, the Eucopiclae, 
indeed, having only one.* 

In the third type, that of the Trachyniedusee, the 




Fig. 53. — Auditory organ of Rhopalonema, still showing a small orifice (after Hertwig). 
hk, Modified tentacle; o, auditory organ. 

auditory organs are modified tentacles. They form a 
club-shaped body, with a central endodermal axis, and 

* Hertwig considers that the supposed hairs shown by Hen sen in 
his figure of the ear of Eucope are really the edges of auditory canals. 



86 



MEDUSiE. 



bearing at the apex one or more sometimes spherical, 
sometimes prismatic, otolithes. In some cases the 
organ becomes enclosed in a cup, which in Geryonia 
closes at the top. 

In another family of the Hydromedusse, the Oceanidae, 
these organs are absent, and appear to be replaced by 
certain pigment spots at the base of the tentacles, 
which, however, from their structure are considered to 
be rudimentary organs of vision, and will be described 
in the chapter on eyes. 

Some species have, in addi- 
tion, other organs, obviously of 
sense, but the function of which 
is still far from clear. Fig. 54 
represents one of these curious 
sense-organs in Pelagia, after 
Hertwig. It is in the form of 
a somewhat bent finger, is 
situated in a deep fold of the 
umbrella, contains a branch of 
the gastro vascular canal, and is 
filled at the tip with a group of 
solid, shining, rod-like crystals. 
The auditory organ in worms 
and molluscs consists of a 
closed vesicle, containing one 
or more otolithes, and lined with nerve-cells, which are, 
in the higher groups, connected at their base with the 
auditory nerve, and bear setae at the other end. De 
Quatrefages was the first who established clearly the 
existence of auditory organs in worms. 

In the Mollusca, the existence of an organ of hearing 
in some Gasteropods was justly inferred by Grant from 




Fig. 54. — Sense-organ of Pelagia 
(after Hertwig). o, Group of 
crystals ; sk, sense-organ ; sf, 
fold of the skin ; ga, gastro-vas- 
cular channel. 



MOLLUSCA— ANNELIDES. 



87 




the fact that one species, Tritonia arbor escens, emits 
certain sounds, doubtless intended to be heard by its 
fellows. 

The cilise contained in the auditory vesicle are some- 
times short, and scattered over 
the general surface, as in Unio 
(Fig. 55) ; sometimes long and 
borne on papillary projections, as 
in Carinaria and Pterotrachea * 
(Fur. 56), where also there are 
certain special cells, supposed to 
act as buffers or dampers. The 
otolithe is sometimes single, and 
nearly spherical, as in Acephala 
and Heteropoda, and consists of calcareous matter with 
an organic base ; in the Gasteropods, Pteropods, and 



Fig. 55. 



„. -Auditory organ of 
IJnio (-Iter Leydig). a, Nerve ; 
h, cells ; c, cilise ; d, otolithe. 




Fig. 56. — Auditory organ of Pterotrachea Friderici (after Claus). Na, Auditory nerve ; 
c, central cells ; d, supporting plate ; b, outer circle of auditory cells ; a, ciliated 
cells. 

some Annelid es (Arenicola, Amphicora) they are 

* Claus., " Ueber den Aconst. App. im Gekororgane der Hetero- 
poden," Arch, fur Mic. Anat., 1878. 
6 



88 



ANNELIDES — CRUSTACEA. 



numerous, and sometimes, as in Cymbulia, collected 
into a mulberry-like group. 

In many cases the auditory sac rests directly on the 
ganglion. 

The actual mode of termination of the nerves is still 
uncertain. I have already mentioned that vibrations, if 
fewer than thirty in a second, do not produce on us the 
effect of sound. But it is possible that these organs in 
the lower animals are intended quite as much to record 
movements in the water as for hearing properly so called. 



The Organs of Hearing in Crustacea. 





Fig. 57. —Base of 
right antermule of 
lobster (Astacus 
marinus) , after 
Farre. a, Orifice ; 

Fig. 5R. — Interior of auditory sac of lobster (after 
Farre). a, Orifice , b, auditory hairs. 

It was long supposed that the auditory organ of the 
Crustacea was situated in the basal segment of the 
outer antenna. The true auditory organ was, indeed, 
discovered by Eosenthal in 1811,* who, however, re- 

* Rett's Arch, fur Phtjs., 1811. 



CRUSTACEA. 89 

garded it as an olfactory organ, as did also Treviranus, 
Fabrieius, Scarpa, Brandt, Milne Edwards, and, in fact, 
the older naturalists generally. The discovery of its 
true nature is due to Farre,* was confirmed by Huxley f 
and Leuckart, and is now generally admitted. It is 
a sac situated in the base, or first segment, of the 
lesser pair of antennae, which is slightly dilated. In 
some species the sac communicates freely with the 

- i 






a 







V m 



Fig. 59.— Part of wall of auditory sac of lobster (Astacus marinus) ; after Eensen. 
a, Thickened bars in the membrane of the sac ; n, first row of auditory hairs ; »', 
second row of auditory hairs ; n", third row of auditory hairs ; r\"', fourth row of 
auditory hairs -, e, grains of sand, serving as otolithes. 

water by means of an orifice situated towards the inner 
and anterior margin, and guarded by rows of fine 
hairs. In others the orifice is closed, but its position 
is always marked, as the auditory sac is at this point 
connected with the skin. 

Both contain otolithes, Those of the closed sacs are 
generally rounded ; while, on the contrary, those of 

* Philosophical Transactions, 1843. 

f Ann. and Mag. of Natural History, 1851. 



90 USE OF GRAINS OF SAND AS OTOLITHES. 

the open sacs are simply grains of sand, and are so 
numerous as sometimes to occupy one-fourth, or even 
one-third, of the sac. 

Farre stated that the otolithes in the auditory sacs 
of Crustacea were simply grains of sand, selected by 
the Crustacea, and put into their own sacs to serve as 
otolithes. It seemed, however, so improbable that 
Crustacea should pick up suitable particles of sand 
and place them in their ears, that the statement was 
not unnaturally received with incredulity. The obser- 
vation of Hensen appears, however, to leave no doubt 
on the subject. The sac, whether open or closed, is an 
extension of the outer skin, and is cast with it at each 
moult. Hensen examined them shortly after moulting, 
and found that the sacs contained no stones ; he saw 
the shrimps carefully selecting particles of sand, but 
could never detect one in the very act of placing 
one in the auditory sac. He therefore placed some 
shrimps in a vessel of filtered sea-water, and strewed 
over the bottom some crystals of uric acid. Soon 
afterwards one of the shrimps moulted, and the auditory 
sac was found on examination to contain a few grains 
of sand, but no crystals of uric acid. Three hours 
later, however, Hensen found that the new sac con- 
tained numerous crystals of uric acid, but none re- 
sembling common sand. Evidently, therefore, the 
Crustacea pick up grains of sand, and actually intro- 
duce them into their own ears to serve as otolithes. 

Otolithes are not, however, universally present. In 
the true crabs (Brachyura) they appear to be always 
wanting, so that the auditory hairs (which present very 
nearly the same character as those of the lobsters, etc.) 
are capable of being thrown into vibrations without the 
mediation of otolithes. 



AUDITOEY HAIRS. 91 

The interior of the sac is thus described by Farre : 
"Along the lower surface of the vestibular sac is seen 
running a semicircular line, broader at its upper than 
its lower extremity (Fig. 58, V). This part is more 
easily examined after the sand has been washed away 
by agitation under water. It is then seen, with a power 
of 18-linear, to consist of several rows of ciliated pro- 
cesses, of which one row is more regular and prominent 
than the rest, and crests the entire margin of the 
ridge. The processes diminish in size and number 
on either side, and are in some places seen in groups, 
but always assume the general form represented in" 
Fig. 58. ' 

In Astacus there are four rows of hairs. The first 
are somewhat scattered, and above the otolithes; the 
second consists of larger hairs, arranged close together; 
the third and fourth are smaller again, and more scat- 
tered. These three rows of hairs are covered by the 
otolithes. They stand in connection with the terminal 
fibrils of the acoustic nerve, and through their vibra- 
tions the sense of sound is supposed to be conveyed. 
In the lobster Hensen counted 548 auditory hairs. 
He divides auditory hairs of Crustacea into three 
classes : otolithe hairs ; free hairs, enclosed in the audi- 
tory sac ; and auditory hairs on the outer body surface. 

These latter auditory hairs (Fig. 59) are situated 
over an orifice in the chitinous integument, and stand 
in direct communication with a fibril from the nerve ; 
the stem of the hair does not rest directly on the 
chitinous integument, but is supported by a delicate 
membrane, which is sometimes dilated at the base ; the 
edge of the chitine at one side of the hair is raised into 
a tooth ; lastly, according to Hensen, each auditory hair 



92 



EAR IN TAIL OF MYSIS. 



possesses a sort of appendage, or languette, to which the 
nerve is attached. 

As far as details are concerned — the 
form of the sac, the number, form, and 
arrangement of the hairs, etc. — the 
auditory organs of the Crustacea offer 
endless variations in the different species, 
while very constant in each. 

In the higher groups the auditory 
sac is always at the base of the small 
antennae. In one of the lower forms, 
however — the curious genus Mysis — 
the ear is situated in the tail. 

The genus Mysis (Fig. 61) is a group 
of Crustaceans, in outward appearance 
very like shrimps, but differing in the 
absence of external gills, and in the 
structure of the legs and other par- 
ticulars, so that it is placed in a different family. Frey 
and Leuekart, moreover, made the interesting discovery 
that it possesses two ears in its tail. 




Fig. 60. — Auditory- 
Lair of the crab 
(Carcinus vicenus), 
X 500. a, Skin ; c, 
nerve ; h, delicate 
intermediary mem- 
brane or hinge (after 
Hensen). 




Fig. 61. — Mysis (after Frey and Leuckart). 

The tail, like that of a lobster, consists of five flaps. 
In each of the two smaller flaps is an oval sac (Fig. 62) 
containing a single, lens-shaped otolithe, consisting of 



MODE OF HEARING. 



93 



a calcareous matter embedded in an organic substance. 
That Crustacea do, as a matter of fact, possess the power 
of perceiving sounds, there can be no doubt. Hensen 
himself has made various experiments on the subject. 
Moreover, strychnine possesses the peculiar property of 
augmenting the reflex power of the nervous centres. 
Taking advantage of this, Hensen placed some shrimps 
in sea-water containing strychnine. He then found 
that they became ex- 
tremely sensitive to even 
very slight noises. Further 
than this, Hensen availed 
himself of Helmholtz's re- 
searches on the perception 
of sound, and, suspecting 
that the different hairs 
might be affected by dif- 
erent notes, found that was 
actually the case. 

The vibration of the hairs 
is mechanical, not depend- 
ing on the life of the 
animal. Hensen took a 
My sis, and fixed it in such a position that he could watch 
particular hairs with a microscope. He then sounded 
a scale ; to most of the notes the hair remained entirely 
passive, but to some one it responded so violently and 
vibrated so rapidly as to become invisible. When the 
note ceased, the hair became quiet ; as soon as it was 
resounded, the hair at once began to vibrate again. 
Other hairs in the same way responded to other notes. 
The relation of the hairs to particular notes is probably 
determined by various conditions ; for instance, by its 
length, thickness, etc. 




Fig. 62. — Tail of My sis vulgaris, show- 
ing the auditory organ. 



94 OEGANS OF HEAKING IN INSECTS. 

That these plumose hairs, then, really serve for hear- 
ing may be inferred, not only from their structure and 
position, but also from the observed fact that they 
respond to sound-vibrations. 

Hensen's observations * have been repeated and 
verified by Helmholtz. 

The Okgans of Heaking in Insects. 

I now pass on to insects. There has been great 
difference of opinion as to the seat of the organ of 
hearing in this group. 

The antennae have, as already mentioned, been re- 
garded as ears by many distinguished authorities, 
including Sulzer, Scarpa, Schneider, Bolk-Hausen, 
Bonsdorff, Cams, Strauss-Diirkheim, Oken, Burmeister, 
Kirby and Spence, Newport, Landois, Hicks, Wolff 
and Graber, who have supported their opinion by 
numerous observations. 

Kirby states that once "a little moth was reposing 
upon my window ; I made a quiet, not loud, but distinct 
noise : the antennae nearest to me immediately moved 
towards me. I repeated the noise at least a dozen times, 
and it was followed every time by the same motion of 
that organ, till at length the insect, being alarmed, 
became more agitated and violent in its motions." 
And again: "I was once observing the motions of an 
Apion (a small weevil) under a pocket microscope ; on 
seeing me it receded. Upon my making a slight 
but distinct noise, its antennae started. I repeated tl e 
noise several times, and invariably with the same 
effect." f 

* " Sensations of Tone." 

t Introduction to " Entomology," Kirby and Spence, vol. iv. 



BEETLES. 95 

Among beetles, the genus Copris, "particularly," says 
Newport, " Copris molossus, in which I first remarked 
it, have the antennae composed of ten joints, the last 
three of which form the knob or club with which it is 
surmounted. 

" When the insect is in motion, these plates or audi- 
tory organs, if we may be allowed so to call them, are 
extended as wide as possible, as if to direct the insect 
in its course ; but upon the occurrence of any loud but 
sudden noise are instantly closed, and the antennae 
retracted as if injured by the percussion, while the 
insect itself stops and assumes the appearance of death. 
A similar use of the antennae is made by another family, 
Geotrupidae, which also act in the same manner under 
like circumstances. 

"These facts, connected with the previous experi- 
ments, have convinced me," he says, "that the antennae 
in all insects are the auditory organs, whatever may 
be their particular structure ; and that, however this 
is varied, it is appropriated to the perception and 
transmission of sound." f 

Will has made some interesting observations on 
some of the Longicorn beetles (Cerambyx), which 
tend to confirm this view. These insects produce 
a low shrill sound by rubbing together the prothorax 
and the mesothorax. The posterior edge of the 
prothorax bears a toothed ridge, and the anterior end 
of the mesothorax a roughened surface, and when these 
are rubbed together, a sound is produced something 
like that made by rubbing a quill on a fine file. 

* Newport, "On the Antennae of Insects," Transactions of the 
Entomological Society, 1856-40, vol. ii. 



96 BEETLES. 

Will took a pair of Cerambyx (beetles), put the 
female in a box, and the male on a table at a distance 
of about fifteen centimetres (four inches). They were at 
first a little restless, but are naturally calm insects, and 
soon became quiet, resting as usual with the antennae 
half extended. The male evidently was not conscious 
of the presence of the female. Will then touched the 
female with a long needle, and she began to stridulate. 
At the first sound the male became restless, extended 
his antennae, moving them round and round as if to 
determine from which direction the sound came, and 
then marched straight towards the female. Will 
repeated this experiment many times, and with dif- 
ferent individuals, but always with the same result. As 
the male took no notice of the female until she began 
to stridulate, it is evident that he was not guided by 
smell. From the manner in which the Cerambyx was 
obviously made aware of the presence of the female by 
the sound, Will considered it clearly proved that in 
this case he was guided by the sense of hearing. 

Will has also repeated with these insects the experi- 
ments I made with ants, bees, and wasps, and found 
that they took no notice whatever of ordinary noises ; 
but when he imitated their own sounds with a quill 
and a fine file, their attention was excited — they 
extended their antennae as before, but evidently per- 
ceived the difference, for they appeared alarmed, and 
endeavoured to escape.* 

Hicks in 1859 justly observed that, "Whoever has 
observed a tranquilly proceeding Capricorn beetle which 
is suddenly surprised by a loud sound, will have seen 

* Will, " Das Geschmacksorgan der Insekten," Zeit. fur. Wiss. Zool. t 

1885. 



SEAT OF THE SENSE OF HEARING. 97 

how immovably outward it spread its antennae, and 
holds them porrect, as it were with great attention, as 
long as it listens, and how carefully the insect proceeds 
in its course when it conceives that no danger threatens 
it from the unusual noise." * 

Other similar observations might be quoted, but 
these suificiently indicate that in some insects, at any 
rate, the organs of hearing are situated in the antennae. 

On the other hand, Lehmann long ago observed 
that the house cricket (Acheta domestica), when 
deprived of its antennae, remained as sensitive* to 
sounds as previously. This is. quite correct; and yet, if 
a cricket be decapitated, and a shrill noise be made 
near the head, the antennae are thrown into vibration 
by each sound. 

In fact, not only do the highest authorities differ, 
but the observations themselves appear at first sight 
to be contradictory. The explanation seems to be that 
the sense of hearing is not confined to one spot. That 
the antennae do serve as ears, at least in some insects, 
the evidence leaves, I think, no room for doubt. But 
there is no reason, in the nature of things, w r hy the 
sense of hearing should be confined to one part of the 
body. Taste, indeed, would be useless except in or 
near the mouth, and almost the same may be said of 
smell. But the sense of touch is spread, in greater or 
less perfection, over the whole skin. Indeed, there is 
among the lower animals a great tendency to repeti- 
tion, and not least so amongst insects. The body con- 
sists normally of a number of segments, each with a 
pair of appendages and a ganglion. There are three 
pairs of legs ; two pairs of jaws, opening, not vertically, 
* Transactions of the Linnean Society, vol. xxii. 



98 DIFFERENT SEATS OF ORGANS OF SENSE. 



as ours do, but laterally; several pairs of breathing- 
holes arranged along the sides of the body ; and two 
kinds of eyes. Moreover, unquestionable organs of 
sense occur in very different parts of the body. The 
Crustacean genus Mysis, as already mentioned, has ears 
in its tail ; one group of sea- worms (the Polyoph- 
thalmata) have a pair of eyes on each segment of the 
body. 

Of Amphicorine, a small worm of our coasts, M. de 
Quatrefages says that often,* "C'est la queue qui marche 
la prgmiere, explorant evidemment le terrain avec une 
grande activite et donnant autant de signes d'intelli- 
gence et de spontaneite que pourrait le faire la partie 
anterieure du corps. . . . Cette queue porte a son 
extremite un disque elargi sur lequel sont places deux 

points rouges. . . . Je ne 
mets nullement en doute que 
ces points ne soient en effet 
des organes de vision." He 
was not able, indeed, to make 
out their finer structure. On 
the other hand, the lateral 
eyes of the Polyophthalmata 
possess a well-formed lens. 

We need not, then, assume 
that the organs of hearing 
in insects must necessarily 
be in the 
that they 
trated in 
body. 
It had long been known that grasshoppers and 




Fig. 63.— Part of leg of Grasshopper 
(Gryllus) ; after Graber. o, t, n, b, 
Tympanum. 



head, or, indeed, 
need be concen- 
part of the 



one 



* Ann. des Set. Nat.. 1850. 



CRICKETS HAVE EAES IN THEIR LEGS. 99 

crickets have on their anterior legs two peculiar, glassy, 
generally more or less oval, drumlike structures ; but 
these were supposed by the older entomologists to 
serve as resonators, and to reinforce or intensify the 
well-known chirping sounds which they produce. 

• Johannes Muller was the first who suggested that 
these drums, or tympana, act like the tympanum of our 
own ears, and that they are really the external parts 
of a true auditory apparatus. That any animal should 
have its ears in its legs sounds, no doubt, a priori 
very unlikely, and hence probably the true function of 
this organ was so long unsuspected. That it is, how- 
ever, a true ear the following particulars, taken 
especially from the memoirs of M tiller,* Siebold,f 
Leydig,f Hensen,§ GraberJ and Schmidt,! conclusively 
prove. 

The Leaping Orthoptera fall into three well-marked 
groups : the locusts (Locustidae), which have short 
antennae; the crickets (Achetidge), which have long 
antennae, and the wings flat on the back ; and, thirdly, 
the Gryllidae, or grasshoppers (as I may perhaps call 
them), which have also long antennae, but in which 
the wings are sloping. This is the nomenclature 
adopted by English authorities, such as Westwood ; 
but unfortunately many foreign entomologists call the 

* " Zur vergleiclienden Physiol ogie des Gesichtsinnes." 1826. 

t "Ueber die Stimm und Gehororgane der Orthopteren," Arch, fiir 
Natur geschichte, 1844. 

% "Ueber Geruchs-und Gehororgane der Krebse und Insekten," 
Reicherts' Arch, fur Anat., 1860. 

§ " Ueber das Gehororgan von Locusta," Zeit. fiir Wiss. Zool., 18G6. 

|| " Die Tympanalen Sinnesapparate der Orthopteren," Arch, fur 
Mic. Anat., vol. xx., 1875. 

If "Die Gehororgane der Heuschrecken," Arch, fiir Mic. Anat, 
vol. xi. 



100 EAK OF GRASSHOPPERS. 

crickets Gryllidce, the grasshoppers Locustidse, and the 
locusts Acridiidee.* 

In grasshoppers (Gryllidae) and crickets (Achetidss) 
the auditory organ lies in the tibia of the anterior leg, 
on both sides of which there is a disc (Fig. 63), generally 
more or less oval in form, and differing from the rest 
of the surface in consisting of a thin, tense, shining 
membrane, surrounded wholly or partially by a sort of 
frame or ridge. In some species the two tympana are 
similar in form ; in others they differ. For instance, in 
the field cricket, the hinder tympanum is elliptic, 
the front one nearly circular in outline. 

In many of the Gryllidae, the tympana are protected 
by a fold of the skin, which projects more or less over 
them. The corresponding spiracle is also specially 
modified in the stridulating locusts, while in those 
which are dumb it is formed in the same manner as 
the others. 

The tympana are not always present, and it is an 
additional reason for regarding them as auditory organs, 
that both among the Achetidse and the Gryllidae, in 
those species which possess no stridulating organs, the 
tympana are also wanting.f 

* The destructive " locust " of the East, which is so numerous that 
in one year our Government 1 in Cyprus destroyed no less than 
150,000,000,000 of eggs, and whose ravages are used in Eastern poetry 
as types of destructiveness, has short antennae, and belongs to the first 
division; to which, therefore, English entomologists apply the name 
Locusta, while our foreign friends, on the contrary, apply the name to 
a totally different insect. However, I merely refer to this now, to explain 
why the terms I have used do not in all cases agree with those 
adopted by the observers to whom I am referring. 

f This rule seems, however, not to be entirely without exceptions. 
At least, Aspidonotus and Hetrodes are said to possess tympana, but 

1 Report on the Locust Campaign, Pari. Paper, 5250 of 1888. 



STRUCTURE OF EAR. 101 

Graber regards the covered tympana as a develop- 
ment from the open ones, and suggests that in time 
to come the species in which the tympana are now 
exposed may develop a covering fold. 

If now we examine the interior of the leg, the trachea 
or air-tube will be found to be remarkably modified. 
Upon entering the tibia it immediately enlarges and 
divides into two branches, which reunite lower down. 
To supply air to this wide trachea the corresponding 
spiracle, or breathing-hole, is considerably enlarged, 
while in the dumb species it is only of the usual size. 
An idea of the form of the trachea will be given by 
Fig. 69, which, however, represents the anterior tibia 
of an ant, where these tracheae are less considerably 
enlarged, and where one of the branches is much smaller 
than the other, while in locusts they are nearly equal 
in width, and one lies against each tympanum. The 
enlarged trachea occupies a considerable part of the 
tibia, and its wall is closely applied to the tympanum, 
which thus has air on both sides of it ; the open air on 
the outer, the air of the trachea on its inner surface. 
In fact, the trachea acts like the Eustachian tube in 
our own ear; it maintains an equilibrium of pressure 

no stridulating apparatus. For instance, in the following forms, both 
the stridulating apparatus and the tympana are absent, viz. : — 

Among the (Ecanthidae : Phalangopsis and Gryllomorpha (both are 
wingless). 

n Platydactylidre : Metrypa and Parametrypa (both wing- 
less). 

?> Tettigonidse : Trigonidium. 

,, Gryllidse : Gryllus apterus, Parahrachytrupes Australis, 
and Apiotarsus (all wingless). 

„ Gryllotalpidse : Tridactylus apicalis. 

)5 Mogoplistidse : Mogoplistes, Myrmecophila, Physoblemma 
(all wingless), and Cacoplistes. 



102 STRUCTURE OF EAR. 

on each side of the tympanum, and enables it freely 
to transmit the atmospheric vibrations. 

These tracheae, though formed on a similar plan, 
present many variations, corresponding to those of 
the tympana, and showing that the tympana and 
the tracheae stand in intimate connection with one 
another. For instance, in those species where the 
tympana are equal, the tracheae are so likewise ; in 
Gryllotalpa, where the front tympanum only is de- 
veloped, though both tracheal branches are present, the 
front one is much larger than the other ; and where 
there is no tympanum, the trachea remains compara- 
tively small, and even in some cases, according to 
Graber, undivided. 

The tibia is thus divided into three parts, as shown 
in the diagram (Fig. 64), the central 

§ portion being occupied by the two 

tracheae (Fig. 64, tr, tr). 
Of the other two spaces, one (the 
■ — ar. . . 

lower one in the figure) is occupied 
tn by the muscles, nerves, etc., while 
the other is mostly filled with blood, 
which thus surrounds and bathes the 
auditory vesicles and rods (ar). 
Fis. 64.— section through The acoustic nerve — which, next 
iweconema, (le | } a °bout to the optic, is the thickest in the 
tracheal? ar, tS^aS body — divides soon after entering 
toryrod * the tibia into two branches; the one 

forming almost immediately a ganglion, the supra- 
tympanal ganglion, to which I shall refer again pre- 
sently; the other passing down to the tympanum, 
where it expands into an elongated flat ganglion, known 
after its discoverer as the organ of Siebold (Fig. 65), 
and closely applied to the anterior tracheae. 



STRUCTURE OF EAR. 



103 



It is well shown in Fig. 65, taken from G-raber. At 
the upper part of the ganglion is a group terminating 
below in a single row of vesicles, the first few of which 




"HTrJ 




Fig. 65. — The tracheae and nerve-end organs from the tibia (leg) of a grasshopper 
(Ephippigera vitium) ; after Graber. EBI, Terminal vesicles of Siebold's organ ; 
hT, hinder tympanum ; Sp, space between the tracheae ; hTr, hinder branch of the 
trachea; SN, nerves of the organ of Siebold; go, supra-tympanal ganglion; 
Gr, group of vesicles of the organ of Siebold ; vN, connecting nerve-fibrils between 
the ganglionic cells and the terminal vesicles ; So, nerve terminations of the organ 
of Siebold ; vT, front tympanum ; vTr, front branch of the trachea. 

are approximately equal, but which subsequently 
diminish regularly in size. Each of these vesicles is 
connected with the nerve by a fibril (Fig. 65, vN), and 
contains an auditory rod (Fig. 66). 



104 AUDITOEY RODS. 

One of these auditory rods is shown in Fig. 66, 
and the general arrangement is shown in the subjoined 
diagrammatic figure (Fig. 67). The rods 
were first described by Siebold, who con- 
sidered them to be auditory from their 
association with the stridulating organs. 
|-fa They have since been discovered in 
many other insects, and may be re- 
garded as specially characteristic of the 
acoustic organs of insects. They are 
brightly refractive, more or less elon- 
gated, slightly club-shaped, hollow (in 
which they differ from the retinal rods), 
and terminate, in Graber's opinion,* in 
a separate end-piece (Fig. 66, ho). In 
^od 6 of — a U gr7J- different insects, besides being in some 
vinwssimus '(after cases more elongated than in others, 
fd\ Auditory toV; they present various minor modifica - 
o, eimma piece. ^- ong j n f orrQj b u t are nearly uniform in 

size — about '016 mm. ; being as large, for instance, in 
the young larva of a Tabanus (2 mm. long) as in 
much larger insects. They are, as we shall see, widely 
distributed in insects, bat as yet unknown in other 
animals. 

At the upper part of the tibial organ of Ephippigera 
there is, as already mentioned, a group of cells, and 
below them a single row (Fig. 65) of cells gradually 
diminishing in size from above downwards. One can- 
not but ask one's self whether the gradually diminish- 
ing size of the cells in the organ of Siebold (Fig. 66) 
may not have reference to the perception of different 

* Graber, u Die chordotonalen Sinnesorgane und das Gehor der 
Insekten," Arch, filr Mic. Anat., 1882. 



POSITION OF AUDITORY RODS. 



105 



notes, as is the case with the series of diminishing 

arches in the organ of Corti (ante, p. 80) of our own ears. 

I have already alluded to the supra-tympanul 

ganglion; this also terminates in a number of vesicles 




Fj(r t 67.— Diagram of a section through the auditory organ of a Grasshopper (Meco- 
nema). c, cuticle; a.r, auditory rod; a.c, auditory cell; tr, tracheae. 

containing auditory rods, which are said to be somewhat 
more elongated than those in the organ of Siebold. 

The arrangement of the organ is very curious, and 
will best be understood by reference to Fig. 68. 

The great auditory nerve, as already mentioned, 
bifurcates almost immediately after entering the tibia, 
and one of the branches swell into a ganglion : from 
this ganglion proceed fibres which enlarge into 
vesicles (Fig. 68), each containing an auditory rod ; and 
then again contract, approximate into a close bundle, 
and coalesce with the hypoderm (inner skin) of the 
w 7 all of the tibia, The supra-tympanal organ of the 
crickets closely resembles that of the grasshoppers, 
while, on the other hand, they appear entirely to want 
the organ of Siebold (Fig. 65). This is a very remark- 
able difference to exist in tw 7 o organs otherwise so 
similar. 

There appear to be two ways in which the atmospheric 



106 



EAR OF LOCUSTS. 



vibrations may be communicated to the nerve: either 
the vibrations of the tympanum may act upon the 
air in the tracheae, and so upon the auditory rods, or 
the air in the tracheae may remain passive, and the 
vibrations may act upon the auditory rods through the 
fluid in the anterior chamber of the leg. The fact 
that the auditory rod is turned away from the tracheae 
would seem to favour this hypothesis. 




[jJZJ^f 



»in 



Fig. 68.— Outer part of a section through the tibia of a Gryllus viridissimus (after 
Graber). h, Hind surface of leg; _p, wall of trachea; F. fat bodies; Su, suspensor 
of the trachea; vW, tracheal wall; TiV, nerve; gz, ganglionic cells; rB, tissue 
connecting the ganglionic cells; E.Sch., end tubes of the ganglionic cells, each 
containing an auditory rod ; fa, terminal threads of ditto. 

In the true Locusticlae (Acridiodeae of Graber) the 
organ of hearing is situated, not in the anterior tibiae, 
but in the first segment of the abdomen ; externally it is 
marked by a glistening appearance, and it is oval, or in 
some cases nearly ear-shaped. It w T as first noticed by 
Degeer. Behind the tympanum is a large tracheal sac, 
as in the families already described, and the tension of 
the tympanum is regulated by one, or in some cases by 
two muscles. The tympanum also presents two chitin- 



EAK OF LOCUSTS. 107 

ous or horny thickenings, a small triangular knob, and 
a larger, somewhat complicated piece, consisting of two 
processes — a shorter upper, and a longer lower one, 
making a broad angle with one another. 

As in the preceding families, so also in the 
Locustidse, the acoustic nerve is in close connection 
with the tracheae; it swells into a ganglion, which con- 
tains in some species as many as 150 auditory rods, and 
then, as in the supra-tympanal organ (see p. 105), con- 
tracts into a tapering end, which is attached to the small 
chitinous knob. The auditory rods differ in no respect, 
as yet ascertained, from those already described. 

For many years no structure corresponding to the 
tibial auditory organ of the Orthoptera w r as known in 
any other insect. 

In 1877, however, I discovered * in ants a structure 
which in some remarkable points resembles that of the 
Orthoptera, and which I described as follows : — " The 
large trachea of the leg (Fig. 69) is considerably 




Fig, 69.— Tibia of yellow ant (Lasius flavus), x 75. S, S, Swellings of large trachea; 
rt, small branch of trachea ; x, chordotonal organ. 

swollen m the tibia, and sends off, shortly after entering 
the tibia, a branch which, after running for some time 
parallel to the principal trunk, joins it again. 

"Now, I observed that in many other insects the 

* Lubbock, " On the Anatomy of Ants,' 1 Microscopical Journal, 

1877. 



108 PECULIAR STRUCTURE IN LEG OF ANT 

tracheae of the tibia are dilated, sometimes with a 
recurrent branch. The same is the case even in some 
mites. I will, however, reserve w 7 hat I have to say on 
this subject, with reference to other insects, for another 
occasion, and will at present confine myself to the ants. 
If we examine the tibia, say of Lasius fiavus, we shall 
see that the trachea presents a remarkable arrange- 
ment (Fig. 69), which at once reminds us of that which 
occurs in Gryllus and other Orthoptera. In the femur 
it has a diameter of about o^^ of an inch ; as soon, 
however, as it enters the tibia, it swells to a diameter 
of about 5^-Q of an inch, then contracts again to g^ , 
and then again, at the apical extremity of the tibia, 
once more expands to g-J^-. Moreover, as in Gryllus, 
so also in Formica, a small branch rises from the upper 
sac, runs almost straight down the tibia, and falls 
again into the main trachea just above the lower sac. 

"The remarkable sacs (Fig. 69, S, 8) at the two 
extremities of the trachea in the tibia may also be well 
seen in other transparent species, such, for instance, as 
Myrmica ruginodis and Pheidole megacephala. 

"At the place where the upper tracheal sac contracts 
(Fig. 69) there is, moreover, a conical striated organ (x), 
which is situated at the back of the leg, just at the 
apical end of the upper tracheal sac. The broad base 
lies against the external wall of the leg, and the 
fibres converge inwards. Indications of bright rods 
may also be perceived, but I was never able to make 
them out very clearly." 

This closely resembles both in structure and position 
the supra-tympanal auditory organ of the Orthoptera. 

Graber has entirely confirmed this account and dis- 
covered some insects in which the structure is more 



ORIGIN OF EAR. 



109 



clearly visible than in any which I had examined. 
Fig. 70 represents part of the tibia of Isopteryx apiealis. 

These organs do not, however, appear to be univer- 
sally present. In some very transparent species no 
trace of them can be found. 

But though so similar in structure, and probably in 










Fig. 70.* — Part of the tibia of Isopteryx apiealis (after Graber). Sc, Auditory organ ; 
ef, terminal filament ; Cu, cuticle ; G, ganglion cells ; ef, terminal filaments ; tr, 
trachea ; n, nerve. 

function, it may be doubted whether this tibial organ 

in the ants can be traced to a common origin with that 

of the Orthoptera. According to Graber, the direction 

of the rods is reversed in the two cases, which he regards 

as clear proofs that they have arisen independently. 

He is even of opinion that the tympana themselves 

have originated independently in the different groups 

of Orthoptera. Moreover, Graber has found this organ 

in certain insects not only in the anterior, but also in 

the two other pairs of legs. Indeed, rods of the same 

character have been found in other regions of the body. 

* In this, as in one or two of the other figures, the explanation of 
some of the lettering appears to be omitted in the original. At least, 
I have been unable to find it. 



110 



EAR OF FLY. 




As long ago as 1764 Keller * observed that the base 
of the curious club-like "halteres," or rudimentary 
hind-wings of flies, "est garnie de poils tres courts, 
ou la tige a le plus d'epaisseur pres du corps ; elle est 
3 inflexible, et presque garrotte par en 

haut de plusieurs nerfs ; en un mot, elle 
est faite de maniere que Ton peut juger 
par sa force par les dehors." This 
observation remained unnoticed, and no 
further description appears to have been 
given of the organ until it was redis- 
covered by Hicks in 1856, and more 
fully described in 1857.f 

He found that though in the Diptera 
(flies and gnats) the hind wings are 
reduced to two minute, club-shaped 
organs, they still receive a nerve which 
is the largest in the insect, except that' 
which goes to the eyes. This proves 
that they must serve some important 
function, and renders it almost certain 
that they are the seats of some sense. 
He also found at the base of the halteres 
a number of " vesicles," arranged in four 
groups, and to each of which the nerve 
sends a branch, though the mode of pre- 
paration which he adopted did not 
permit him to see the finer structure of the nerves, 
which he figures as mere fine, hard lines. He describes 
the " vesicles " as " thin, transparent, hemispherical, or 



\ 




Fig. 71.— One of the 
halteres of a fly 
(after Lowne). 



* "Geschichte der gemeinen Stubenfliege," 1764. I have not seen 
the original, and quote from Hicks's paper. 

t Transactions of the Liunean Society, vol. xvii. 



PECULIAE SENSE-ORGANS. Ill 

more nearly spherical projections from the cuticular 
surface," and as placed in rows. The number and 
arrangement differ in different species: the blowfly 
(Sarcophaga carnaria) has ten rows, Syrphus luniger as 
many as twenty. 

These organs have recently been again examined by 
Bolles Lee.* The vesicles are, according to him, un- 
doubtedly perforated, contain a minute hair, and those 
of the upper groups are protected by hoods of chitine. 
He inclines to correlate them with the similar antennal 
organs, which he regards as olfactory. His view of the 
minute structure of these rods differs from that of 
previous authors, and the subject requires further 
study. 

He finds, moreover, that the sense-organ containing 
the rods has nothing to do with the vesicular plates, 
but that they are attached to the cuticle in a different 
place, and where it presents no special modification. 

The numerous small membranes in the hal teres of 
insects seem to bear somewhat the same relation to 
the single tympanum of, say, the locust, as the many- 
faceted eyes do to those with a single cornea. The 
head of the halteres is divided into two separate 
spaces by a membrane composed of elongated hypo- 
dermal cells. The upper part contains a number of 
large vesicular cells, like those w T hich are in connection 
with the ends of the tracheae. It does not appear 
to contain any special sense-organ, and, in fact, the large 
nerve is almost entirely devoted to the sense-organs at 
the base. M. Bolles Lee suggests that it perhaps 
serves principally to regulate the pressure on these 
delicate structures. 

* "Les Balanciers des Dipteres," Becueil Zool. Suisse, 1885. 
7 



112 AUDITORY RODS IN BEETLES. 

Special sense-organs occur also on the wings of other 
insects. Hicks found them " most perfect in the Diptera, 
next so in the Coleoptera, rather less so in the Lepidop- 
tera, but slightly developed in the'Neuroptera, scarcely 
at all in the Orthoptera (though this assertion may be 
hereafter modified), and that only a trace of them exists 
in the Hemiptera." They are similarly constituted and 
equally developed in both sexes. Hicks regarded them 
as organs of smell. Leydig,* on the contrary, considered 
them as auditory organs. His mode of preparation dis- 
played better the structure of the nerves, and he found 
that they end in peculiar, club-shaped rods (Stabehen 
oder Stafle), closely resembling those in the ears of 
Orthoptera. He observes that, as in the case of the 
tibial auditory rods of Orthoptera these rods are of 
two sorts, which are arranged separately, those in one 
part of the organs being shorter and blunter, those in 
another more pointed and elongated. Bolles Lee, on 
the contrary, considers that the supposed existence of 
two forms, pointed and rounded, is merely due to an 
optical deception, and that in reality they are all 
similar. Leydig also observed in some cases that the 
rods were thrown into fine ridges. He found also 
somewhat similar papillae on the front wings of certain 
insects, but could not detect in them the characteristic 
nerve-ends. It must be confessed that the base of the 
wing would not seem a convenient place for an organ 
of hearing. The movements of the wing, it might 
well be supposed, would interfere with any delicate 
sensations. Still, this objection would apply to almost 
any sense being thus placed. 

" Auditory rods " are now, moreover, known to occur 

* Mullens Archiv., 1860. 



POSITION OF AUDITORY RODS. 113 

in other parts of the body ; for instance, they have been 
discovered in the antennae of a water-beetle (Dytiscus) 
and of Telephorus by Hicks, Leydig, and Graber, and in 
the body segments of several larvae by Leydig, Weiss- 
mann, Graber, Grobben, and Bolles Lee. In the larva 
of Dytiscus, indeed, they have been observed in the 
body, antennae, palpi, under lip, and legs. Moreover, 
while, as we have seen, in the tibiae of Orthoptera 
and the halteres of flies they are numerous, in some of 
these cases they are few, sometimes, indeed, only a 
single rod being present, as discovered by Grobben in 
Ptychoptera.* Nevertheless the evidence that they 
are really acoustic organs is, in the case of the 
Orthoptera, so strong, their structure is so peculiar, 
and the gradation of these organs from the most com- 
plex to the most simple is so complete, that it seems 
reasonable to attribute to them the same function. 

Moreover, as regards the very simplest forms there is 
another consideration pointing to this conclusion. We 
have seen that in the Orthoptera the terminal filaments 
close up, and are attached to the skin. Now, it seems 
to be a very general rule, in reference to these organs, 
that they are attached to the skin at two points, 
between which is situated the attachment of the nerve. 
These points, moreover, are so selected as to be main- 
tained at the same distance from one another, thus pre- 
serving an equable tension in the connecting filament. 

Fig. 72, for instance, represents part of one segment 
of the body of the larva of a gnat (Oorethra). This larva 
is as transparent as glass, and very common in ponds, 
a most beautiful and instructive microscopic object. 
EG is the ganglion ; a is the nerve in question, which 

* Sitz. der K. AJcad. der Wiss. Wien, 1876, 



114 CHORDOTONAL ORGAN OF GNAT-LARVA. 

swells into a little triangular ganglion at g; from g 
the auditory organ runs straight to the skin at e, 
and contains two or three auditory rods (not, how- 
ever, shown in the figure) at the point Chs; in the 
opposite direction, a fine ligament passes from g to the 

EG tV^/^^^^?|[ ttu 




Fig. 12.— Right half of eighth segment of the body of the larva of a gnat (Corethra 
plumicornis) ; after Graber. EG. Ganglia; N, nerve; g, auditory ganglion; 
gb auditory ligament ; Chs, auditory rods; a, auditory nerve; e, attachment o 
auditory organ to the skin , b, attachment of auditory ligament to the skin ; 
hn, hn\ termination of skin-nerve; tb, plumose tactile hair; h, simple hair; 
tg, ganglion of tactile hair; Zm, longitudinal muscle. 

skin at b. Hence the organ ge is suspended in a 
certain state of tension, and is favourably situated to 
receive even very fine vibrations.* 

There are, as we have seen, a large number of 
observations which point to the antennae as organs of 
hearing, and many more might have been given. 
When w 7 e come to consider, however, the anatomical 
provision which renders the perception of sound 

* Similar organs occur in other insects, as, for instance, in Ptychoptera. 



AUDITOKY HAIRS ON ANTENNAE OF GNAT. 115 

possible, we are met by great difficulties. The evidence 
is, I think, conclusive that the antennae are olfactory 
as well as tactile organs, and I believe that they serve 
also as organs of hearing. There are, moreover, as 
shown in the last chapter, various remarkable structures 
in the antennae, and I have given reasons for thinking 
some of them to be the seat of the sense of smell. 
Which, if any, of the remainder convey the sense of 
sound, it is not easy to determine. I have suggested 
that Hicks's bottles (Fig. 43) may act as microscopic 
stethoscopes ; * but they occur, so far as we at present 
know, only in ants and certain bees. 




Fig. 73.— Head of gnat. 

That some of the antenna! hairs are auditory can, 
I think, no longer be doubted, Johnson, whose figure 
I give (Fig. 73), suggested! in 1855 that the hairs on 
the antennae of gnats serve for hearing. Mayer also,! 

* I am glad to see that Leydig, who, however, does not appear to have 
read either Hicks's paper or mine, also regards these as chordotonal 
organs (Zool. Anz., 1886). 

t Quarterly Journal of Microscopical Science, 1855. 

% American Journal of Science ani Arts, 1874, 



116 SYMPATHETIC VIBRATIONS. 

led by the observations of Hensen, has made similar 
experiments with the mosquito, the male of which has 
beautifully feathered antennae. He fastened one down 
on a glass slide, and then sounded a series of tuning- 
forks. With an Ut 4 fork of 512 vibrations per second 
he found that some of the hairs were thrown into 
vigorous movement, while others remained nearly 
stationary. The lower (Ut 3 ) and higher (Ut 5 ) harmo- 
nics of Ut 4 also caused more vibration than any 
intermediate notes. These hairs, then, are specially 
tuned so as to respond to vibrations numbering 512 
per second. Other hairs vibrated to other notes, 
extending through the middle and next higher octave 
of the piano. Mayer then made large wooden models 
of these hairs, and, on counting the number of vibra- 
tions they made when they were clamped at one end 
and then drawn on one side, he found that it " coincided 
with the ratio existing between the numbers of vibrations 
of the forks to which co-vibrated the fibrils." It is 
interesting that the hum of the female gnat corresponds 
nearly to this note, and would consequently set the 
hairs in vibration. 

Moreover, those auditory hairs are most affected 
which are at right angles to the direction from which 
the sound comes. Hence, from the position of the 
antennae and the hairs, a sound will act most intensely 
if it is directly in front of the head. Suppose, then, 
a male gnat hears the hum of a female at some little 
dLtance. Perhaps the sound affects one antenna more 
than the other. He turns his head until the two 
antennae are equally affected, and is thus able to 
direct his flight straight towards the female. 

The auditory organs of insects, then, are situated in 



ORGANS OF HEARING IN VARIOUS PARTS OF BODY. 117 

different insects in different parts of the body, and 
there is strong reason to believe that even in the same 
animal the sensitiveness to sounds is not necessarily 
confined to one part. In the cricket, for instance, the 
sense of hearing appears to be seated partly in the 
antennae, and partly in the anterior legs. In other 
cases, as in Corethra, the division appears to be carried 
still further, and a " chordotonal " organ occurs in each 
of several segments. 

No doubt the multiplication of complex organs, like 
our ears, arranged as they are to appreciate a great 
variety of sounds, would be so great a waste that any 
theory implying such a state of things would be quite 
untenable ; but with simple organs, such, for instance, 
as that of Corethra * (gnat ; Fig. 72), the case is 
different, and there would seem to be an obvious 
advantage in such organs occurring in different parts 
of the body, ready to receive sound-waves coming from 
different directions. Moreover, the different organs 
exist ; they do not appear to be organs of touch, yet 
they are clearly organs of sense, and that sense, what- 
ever it be, whether hearing or any other, and though 
it may well be simple, and even perhaps confused, 
must be seated in various parts of the body. The fact 
of their being so distributed does not make it more 
improbable that they should be organs of hearing, than 
of any other sense. 

At the same time, it is an interesting result of recent 
investigations that the auditory organs of insects are 
not only situated in various parts of the body, but are 
constructed on such different principles. 

* Where, however, the number does not approach to that in certain 
Medusae (see ante, p. 84). 



CHAPTER VI. 

THE SENSE OF SIGHT. 

It might at first sight seem easy enough to answer the 
question whether an animal can see or not. In reality, 
however, the problem is by no means so simple. We 
find, in fact, every gradation from the mere power of 
distinguishing a difference between light and darkness 
up to the perception of form and colour which we 
ourselves enjoy. 

The undifferentiated tissues of the lower animals, 
and even of plants, are, as we all know, affected in a 
marked manner by the action of light. 

But to see, in the sense of perceiving the forms of 
objects, an animal must possess some apparatus by 
means of which — firstly, the light coming from different 
points, a, b, e, d, e, etc., is caused to act on separate 
parts of the retina in the same relative positions ; and 
secondly, by means of which these points of the retina 
can be protected from the light coming in other 
directions. 

There are three modes in which it is theoretically 
possible that this might be effected. 

Firstly, let 8 8 f be an opaque screen, with a small 
orifice at o. Let a b c d e be a body in front of the 



THREE POSSIBLE MODES OF SIGHT. 



119 



screen. In this case the rays from the point e can 
pass straight through the orifice o, and fall on the 
retina of an eye, or on a flat surface at c'. There is 
no other direction in which the rays from c could pass 
through o. In the same way, 
the light from a would fall on 
the point a\ that from b on V, 
froin d on d', and e on e'. 

The results which would be 
given in this way would be, 
however, very imperfect, and, 
as a matter of fact, no eye con- 
structed on this system is 
known to exist. 

Secondly, let a number of 
transparent tubes or cones with opaque walls be ranged 
side by side in front of the retina, and separated from 
one another by black pigment. In this case the only 
light which can reach the optic nerve will be that which 
falls on any given tube in the direction of its axis. 





Fig. 75. 



For instance, in Fig. 75 the light from a will pass to a', 
that from b to b\ that from c to c', and so on. The 
light from c, whL-h falls on the other tubes, will not 



120 DIFFERENT FORMS OF EYE. 

reach the nerve, but will impinge on the sides and be 
absorbed by the pigment. Thus, though the light 
from c will illuminate the whole surface of the eye, it 
will only affect the nerve at d . 

In this mode of vision, which was first clearly 
explained by Johannes Miiller, the distinctness of the 
image will be greater in proportion to the number of 
separate cones. "An image," he says,* "formed 'by 
several thousand separate points, of which each corre- 
sponds to a distinct field of vision in the external 
w r orld, will resemble a piece of mosaic work, and a 
better idea cannot be conceived of the image of 
external objects which will be depicted on the retina 
of beings endowed with such organs of vision, than by 
comparing it with perfect work of that kind." 

There is, it will presently be seen, reason to suppose 
that the compound eyes of insects, Crustacea, and 
some molluscs, are constructed on this plan. 

Thirdly, let L (Fig. 76) be a lens of such a form 



. \V^ 




F.g. 76. 

that all the light which falls upon its surface from the 
point a is re-collected at the point a\ that from b at b\ 
from g at d, and so on. If now other light be excluded, 

* * Phys. of the Senses," by Johannes Miiller, translated by Dr. 
Baly. 



THE VERTEBRATE EYE. 



121 



an image of a b c will be thrown on a screen or on a 
retina at d V c'. The image, it will be observed, is 
necessarily reversed. This is the form of eye which 
we possess ourselves : it is, in fact, a camera obscura. 
It is that of all the higher animals, of most molluscs, 
the ocelli of insects, etc. 

Fig. 77, taken from Helmholtz, will give an idea of 
the manner in which we see. 




Fig. 77.— G, Vitreous humor; L, lens; W, aqueous humor; c, ciliary process; d, 
optic nerve ; e e, suspensory ligament ; k fe, hyaloid membrane ; / f, h h, cornea ; 
g g, choroid; i, retina; I I, ciliary muscle; mf, nf, sclerotic coat; p p, iris; s, 
the yellow spot. 

The eyeball is surrounded by a dense fibrous mem- 
brane, the sclerotic coat, or ivliite of the eije, mf, nf which 



122 STRUCTURE OF THE EYE. 

passes in front into the glassy, transparent cornea,//, 
h h ; the greater part of the centre of the eye is occupied 
by a clear gelatinous mass, the vitreous humor, G, in 
front of which is the lens, L ; while between the lens and 
the cornea is the aqueous humor, W. The sclerotic 
coat is lined at the back of the eye by a delicate, 
vascular, and pigmented membrane — the choroid, g g, so 
called from the great number of blood-vessels which it 
contains ; in front this membrane joins the iris, p p, 
which leaves a central opening, the pupil, so called 
from the little image of ourselves, which we see re- 
flected from an eye when we look into it. The iris gives 
its colour to the eye, its posterior membrane con- 
taining pigment-cells ; if these are few in number, it 
appears blue, from the layer behind shining through, 
and the greater the number of these cells the deeper 
the colour, e e, is a peculiar membrane, which serves to 
retain the lens in its place. The optic nerve, d, enters 
at the back of the eye, and, spreading out on all sides, 
forms the retina, i, of which one spot, s, the yellow spot, 
is pre-eminently sensitive. The action of the eye re- 
sembles that of a camera obscura, and, as shown in 
Fig. 76, the rays which fall upon it are refracted so 
as to form a reversed picture on the back of the eye. 

The retina (Fig. 78) is very complicated, and, 
though no thicker than a sheet of thin paper, consists 
of no less than nine separate layers, the innermost 
(Figs. 78, 79) being the rods and cones, which are the 
immediate recipients of the undulations of light. 
Fig. 79 represents the rods and cones isolated and 
somewhat more enlarged. 

The number of rods and cones in the human eye is 
enormous. At a moderate computation the cones may 



THE RETINA. 



123 



be estimated at over 3,000,000 ; and the rods at 
30,000,000.* 




Fig. 78. — Section through the retina (after Max Schultze). Beginning from the outside, 
1, limitary membrane ; 2, layer of nerve-fibres ; 3, layer of nerve-cells ; 4, nuclear 
layer ; 5, inner nuclear layer ; 6, intermediate nuclear layer ; 7, outer nuclear 
layer ; 8, posterior membrane ; 9, layer of small rods and cones ; 10, choroid. 

* Sulzer estimates the cones at 3,360,000 ; Krause places the cones 
at 7,000,000, the rods at 130,000,000 ; but Professor M. Foster tells me 
that he thinks the latter figure is too high. 



124 



THE RODS AND CONES. 



It will be observed that the nerve does not, as one 
might naturally have expected, enter the eye and then 
spread itself out at the back of the retina ; but, on the 

contrary, pierces the retina 
and spreads itself out on the 
front, so that the cones and 
rods look inwards, and not 
outwards — towards the back 
of the eye, and not at the 
object itself. In fact, we do 
not look outwards at the 
actual object, but we see the 
object as reflected from the 
base of our own eye. 

From the arrangement of 
the rods in the eyes of verte- 
brata, then, the light has 
necessarily to pass through 
the retina, and is then re- 
flected back on it. This 
involves some loss of light ; 
on the other Land, it perhaps 
secures the advantage that 
the sensitive terminations of 
the rods and cones can be 
more readily supplied with 
blood. 

I do not propose to enter 
into the reason for this 
peculiar arrangement, which 
is connected with the development of the eye. But 
it is so different from what might have been expected, 
is in itself so interesting, and makes so important a 




Fig. 79. — A, Inner segments of rods 
(s, s, s) and cones (z, z') from man, 
the latter in connection with the 
cone- granules and fibres as far as 
the external molecular layer, 6. In 
the interior of the inner segment of 
both rod and cone fibrillar structure 
is visible. X 8U0. 



THE BLIND SPOT IN THE EYE. 



125 



contrast with the form which is general, though not 

universal among the lower animals, that I think it 

will not be out of place to 

mention a very simple and 

beautiful experiment by 

which every one can satisfy 

himself that it is so. 

One result is that we have 
in each eye a blind spot, that 
at which the nerve enters. 
Tarn the present page, so 
that the white circle is in 
front of the left eye and the 
small cross in front of the 
right. Then close the right 
eye, look steadily across at 
the cross with the left, 
and move the book slowly 
backwards and forwards. 
At one particular distance, 
about ten inches, the white 
circle will come opposite 
the blind spot and will 
instantaneously disappear. 
Across an ordinary room, if 
a man stands in front of a 
screen, his head may in the 
same way be made entirely 
to vanish. 

The ordinary vertebrate 
eye consists of two main 
divisions : the refractive Fig. so. 

part, which is a modified portion of the skin ; and the 




126 INVERSION OF THE RODS. 

receptive part, which arises from the central nervous 
system ; and the inverted arrangement of the rods is, 
we can hardly doubt, connected with the develop- 
ment of the eye, though it is not yet, I think, satis- 
factorily explained. 

There is, however, another eye in vertebrates, with 
reference to which I must say something, and which, 
though now rudimentary, is most interesting. Our 
brain contains a small organ, about as large as a hazel- 
nut, known, from its being shaped somewhat like a cone 
of a pine, as the pineal gland. Its function has long 
been a puzzle to physiologists. Descartes suggested 
that it was perhaps the seat of the soul ; and though 
this idea, of course, could not be entertained, no 
suggestion even plausible had been made. 

So matters stood until quite recently, when a most 
unexpected light has been thrown upon the question. 
As long ago as 1829, Brandt, describing the skull of 
a lizard (Laeerta agilis), pointed out that in the 
centre of the top of the head was a peculiar spot, one 
of the scales being quite unlike the rest. Leydig* 
subsequently observed that on the head of the slow- 
worm (Anguis fragilis) there is a dark spot surrounding 
a small unpigmented body immediately over the pineal 
gland. Rabl-Kuckhard,f in 1884, again called atten- 
tion to this structure, and suggested that it might 
serve for the perception of warmth. Ahlborn,$ in the 
same year, was the first to suggest that it was a 
rudimentary eye. De Graaf § has the merit of dis- 

* " Die Arten der Sanrier." 

t " Entw. des Knochenfischgehirn," Bericht der Sitz. naturf. Freunde. 
Berlin: 1882. 

t "Ueber d. Bedeutung der Zirbeldruse," Zeit.fur Wiss. Zool, 1884. 

§ "Zur. Aiiat. und Ent. der Epi.b. Ainphi'>ien und Reptilien," Zool. 
Anz., 18S6. 



THE PINEAL GLAND. 127 

covering that in the slow-worm the pineal gland is 
actually modified into a structure resembling an inver- 
tebrate eye. This remarkable structure has since been 
examined in various Eeptilia by Mr. Spencer.* It 
appears to be more highly organized in Hatteria than 
in any other form yet studied ; but the retrogression of 
the different structures has not proceeded pari passu, 
in some cases the lens, in some the retina, in others 
the nerve, having been most modified, or having dis- 
appeared. In Hatteria and Varanus the eye is very 
distinct ; the interior parts being more perfect in the 
former; while in the latter it is externally most con- 
spicuous, standing out prominently from its creamy 
whiteness. The lens is cellular in structure, and thins 
away rapidly at the sides. The "rods" are well 
developed, and embedded in pigment. 

Spencer describes the various modifications of the 
organ in the iguanas, chame- , 

leons, flying lizards, geckos, etc. 

Fig. 81 represents the ex- 
ternal aspects of the eye-scale 
in a small lizard (Calotis), with 
the transparent cornea in the 
middle, through which the eye 
is seen; and the diagram 
Fig. 82 a section through 
the eye-scale of a small lizard 
(Lacerta). _,. Q1 _,. , 

v y lig. 81. — Pmeal eye-scale on the 

A very interesting: point in h ^ ad of a sma11 lizard (Caiotis) ; 

J o i after Spencer. 

connection with the piueal eye 

consists in the fact that the optic nerve does not 

penetrate the retina, and then spread out on its outer 

* Quarterly Journal of Microscopical Science, October, 1886. 




128 THE KUD1MENTARY MEDIAN EYE. 

surface, as in the lateral eyes of all vertebrates, but, on 
the contrary, is distributed over its exterior surface. It 
is, therefore, as De Graaf pointed out, formed in this 
respect on the type of the usual invertebrate eye ; so 
that we have the remarkable fact that in the same 




Fig. 82. — Diagram of a section through the skull and pineal eye of Lacerta viridis. 
C, Cuticle; Pa, parietal bone; Ep, epidermis; L, lens; Pig, Pigment; R, rete 
muscosum ; CH, cerebral hemisphere ; N, nerve ; E.p, epiphysis ; OpL, optic lobe 
of brain. 

vertebrate animal we find eyes formed tm two different 
types. Not only so, but the development is dissimilar, 
the lens of the pineal eye being formed out of the 
walls of the neural canal. So that the lens of the 
pineal eye is a totally different structure from that of 
the lateral eyes. 

Spencer observed no effect whatever when he threw 
a strong light on the pineal eye. In fact, he does not 
believe that in any of the species examined by him 
the organ is at present in a functional condition. 
Indeed, in some cases the cornea is quite opaque, and 
in others the nerve to the brain is not continuous ; so 
that there can be no vision. At the same time, it 
seems to be established that this organ is the degraded 
relic of what was once a true eye. 

From the size of the pineal orifice in the skull of 



THE MEDIAN VERTEBRATE EYE. 129 

the huge extinct reptiles, such as Ichthyosaurus and 
Plesiosaurus, it has been, I think, fairly inferred that 
the pineal eye was much more developed than in any 
known living form. 

In living fish and Amphibia, so far as they have been 
yet examined, the organ is even more rudimentary 
than in reptiles. But in the fossil Labyrinthodonts the 
skull possesses a large and well-marked orifice for the 
passage of the pineal nerve. This orifice is, in fact, 
so large that it can scarcely be doubted that the eye in 
these remarkable amphibia was also well developed, 
and served as a third organ of vision. 

In birds the organ is present, but retains no re- 
semblance to an eye. It is solid and highly vascular. 
In mammals it is still more degenerate, though a trace 
is still present even in man himself. 

The larval Ascidians, which present so many points 
of resemblance to the lowest vertebrates, and especially 
to the Lancelet (Amphioxus), have hitherto been re- 
garded as differing from them in the possession of a 
central eye. It now, however, appears that the verte- 
brate type did originally possess a central eye, of which 
the so-called pineal gland is the last trace. 

It seems, then, very tempting to regard the pineal 
eye as representing the central eye of Amphioxus; 
but Spencer points out that the two organs differ 
greatly in structure, and he himself doubts whether 
the pineal eye is really the direct representative of the 
central eye in the Tunicata. 

Beraneck* also regards the pineal as entirely 
different from the central eye of the Tunicata. Indeed, 
he considers its differentiation as an eye to be a 

* "Ueber d. Parietal Auge der Reptilien," Jenaische ZeiL, 1887. 



130 ORGANS OF VISION IN THE LOWER ANIMALS. 

secondary modification, and considers that it had 
previously served some other function. 

However this may be, it cannot be doubted that the 
pineal gland in Mammalia is the representative of the 
cerebral lobe which supplies the rudimentary pineal 
eye of Beptilia, and this itself is probably the degenerate 
descendant of an organ which in former ages performed 
the functions of a true organ of vision. 



The Organs of Vision in the Lower Animals. 

Mere sensibility to light is possible without any 
optical apparatus. Even plants, as we know r , can well 
distinguish between light and darkness; and though 
it seems that in our own case the general surface of 
the skin has lost its sensitiveness to light, still, in many 
of the lower animals, light seems to act generally and 
directly on the tissues. 

Some microscopic vegetable forms even, as, for in- 
stance, Englena (Fig. 83), possess a red spot,* which 

appears to be specially sensi- 
tive to light. 

The lower animals are, in 
a great many cases, very 
transparent. Light passes 
' rig. ^.-Engiena viridis. easily through them, and, 
e, Eye-spot. except in so far as it is ab- 

sorbed, can hardly be supposed to produce any effect. 
The most rudimentary form of a light-organ, then, may 
be considered to be a coloured spot. 

In the first chapter I have endeavoured to show how 

* The moving zoospores of certain algae also possess a red spot, 
which may perhaps have special reference to light. 




COLOR-SPOTS. 



131 



it may be possible to trace an almost complete series 
from such a mere spot of colour in the skin up to a 
complex organ of vision, such, for instance, as that of 
a snail ; indeed, in the development of the eye in the 
individual animal may be traced some of the same stages 
as have probably been passed through by the ancestral 
forms of the animal itself in long bygone ages. 

We must not, however, suppose that all eyes can be 
traced back to one and the same origin, or have been 
developed in the same manner. There are even cases 
in which an organ fulfilling a different function appears 
to have been modified into an eye. 

Look, for instance, at the organ of touch of 
Onchidium* (Fig. 16). The cuticle (see p. 14) is 
thickened into a biconvex, almost lens-like body ; the 
epithelial cells are elongated, and below is a mass of 
cells, to which runs a nerve. A very little change 
would make this an organ capable of distinguishing- 
light from darkness, and n j 
some of the eyes of On- 
chidium appear, indeed, 
to have thus originated. 

Compare with this, for 
instance, the ocellus of 
the young larva of a 
water-beetle (Fig. 84), 
as figured by Grenacher. 

The eye-spots of Me- 
dusao were first noticed 
by Ehrenberg in 1836, 
and the lens was discovered many years afterwards by 
de Quatrefages. It is, in fact, by no means universally 

* A slug-like genus of molluscs. 




Fig. 84. — Section through the simple eye of 
a young Dytiscus larva (after Grenacher). 
I, Corneal lens ; g, cells forming the vitreous 
humor ; r, retina ; o, optic nerve ; h, hypo- 
derm. 



132 



ECHINODERMS. 



present; the eye, if so it can be called, in many species 
consisting merely of a coloured spot, while in others 
it is entirely absent.* 





Fig. 85.— Eye-spot of Lizzia (after 
Hertwig). oc, Ocellus ; I, lens. 



Fig. 86.— Eye-bulb of Astropecten (after 
Haeckel). 



In the Echinoderms, the eyes, which were discovered 
bv Ehrenberg, have been described by Haeckel,t 
Wilson,f Lange, and others. § They are in some cases 
situated, as in Astropecten, on a pear-shaped bulb 
(Fig. 86). 

They consist of a lens (Fig. 87), supplied with a 
nerve, and lying in a mass of pigment. In Solaster or 

* Allman, " Mon. of the Hydroids," Ray Society, 1871. 
f "Ueber die Augen und N erven der Seesterne," Zeit. fur Wiss. 9 vol. x. 
X Transactions of the Linnean Society. 

§ Lange, " Beit. z. Anat. und Hist, der Asterien und Ophiuren," 
Morph. Jahrbuch, 1876. 



WORMS. 



133 




Fig. 87.— Eye of Asteracanthion (after 
Haeckel). c, Cuticle ; e, epithelium ; 
I, lens ; p, pigment. 



Asteracanthion the lenses look like brilliant eggs, 
" each in its own scarlet nest." 

In some species there are as many as two hundred 
eyes; but there appears to 
be no retina, so that they 
can do little more than dis- 
tinguish between light and 
darkness. 

It is quite possible that in 
some of the lower animals, 
where the eye-spot is sup- 
posed to consist merely of a 
layer of pigment at the end 
of a nerve, a lens may here- 
after be discovered. 

In the Turbellaria* the 
eyes, which were first noticed 
by de Quatrefages, are numerous, and lie immediately 
under the epithelium (skin). They consist of a certain 
number of crystalline rods and corresponding retinal 
cells, resting on a cup-shaped bed of pigment, and con- 
nected with a nerve. There is often a group on each 
side of the head, immediately over the brain. In 
species which possess tentacles the eyes are generally 
combined with them ; in others they are scattered over 
the whole periphery of the body, and look in all direc- 
tions. They differ greatly in size, and in the number 
of rods and retinal cells — the larger tentacular eyes 
having several; the small, scattered ones, which are 
generally more deeply situated, even as few as two or 
three. 

* "Die Polycladen," Fauna mid Flora des Golfes von Neapel, 1884. 
Carriere, " Die Augen von Planaria," Arch, fiir Mic. Anat., 1882. 



134 WORMS. 

In most of the Annulata (worms), the eyes, so far as 
they have yet been described, are very simple, and 
probably in most cases not capable of giving more than 
a mere impression of light. In some species the eye- 
spot is merely a group of pigmented epithelial cells. 
Iq many (Fig. 87) there is, besides the pigment, a 
well-marked lens. At the same time, it is probable 
that in some cases this supposed simplicity is more 
apparent than real. The dioptric part is often cellular, 
consisting sometimes of one cell, sometimes of several. 
They are generally, but not always, situated on the 
head. The Polyophthalmians (Fig. 90), as already 
mentioned, have a series along the sides of the body, 
in pairs from the seventh to the eighteenth segments. 
I agree with Carriere that there is no sufficient reason 
for considering the supposed "eyes" of the leech as 
organs for the perception of light, but other species 
of the same group (Clepsine) possess well-marked, 
though rudimentary eyes.* 

Certain leeches — for instance, Piscicola respirans — in 
addition to the pigmented spots on the head, have also 
some on the posterior sucking disc. These somewhat 
resemble the supposed organs of touch, but are larger, 
and surrounded by pigment. There is no lens, but the 
large cells are very transparent. It is not supposed 
that they give any distinct image, or can do more than 
distinguish light from darkness — as Leydig says, 
" feel " the light. Still, I must confess that the deter- 
mination of these curious organs as eyes seems to me 
very doubtful. 

Fig. 88 represents the anterior extremity of a small 
freshwater worm (Bohemilla). 

* Graber, "Morph. Unt. fiber die Augen der frei-lebenden Borsten- 
wiimier," Arch, fur Mic. Anat., 1880. 



WORMS. 



135 



Fig. 89 represents an eye-dot of Nereis. In this 
genus there are two pairs of eyes, which differ some- 






Fig. 88. — Anterior extremity of a freshwater worm (Bohemilla comata)-, after 
Vejddvsky).* a, Eye; b, brain, c, cuticle; hp, hypoderm; lb, tactile hair* 
ne^ nerve , v. blood-vessei. 

what in structure, the lens in the anterior pair being 
flatter, that in the posterior more conical. In Hesione 
the difference is even more 
marked. f In Polyophthalinus, 
besides the eyes in the head, 
there is, as already mentioned, 
a series along the sides of 
the body, which differ some- 
what in structure from those 
in the head. 

As a general rule, in the Annelids each eye contains 
a single lens, but the cephalic eyes of Polyophthalmus, 
according to Mayer, contain three. 

* "Sys. und Morph. der Oligochseten." 

t G-raber, <% Morph. Unt. iiber die Augen der frei-lebenden Borsten- 
wurmer," Arch fur Mic. Anat, 188U. 
8 



Fig. 89.— Eye-dot of Nereis (after 
Miiller). * In B the pigment is 
partly removed so as to show 
the lens. 



136 



WORMS. 



St Stm,! 1 

i,oi. 




Fig. 90.— The first twelve segments of Polyophthalmus pictus, seen from below (after 
xWayer). The Roman numerals indicate the segments. St, Papilla? on the head; 
KS, head; au, head eve; s.au, side eyes; 01, upper lip; Ul, under lip; v. ph. 
pharyngeal vein ; V.suUnta, anterior ventral vein ; V.d.V-\ veins connecting the 
superior lateral and vessels ; sept 1 - 3 , intersegmentary membranes ; m.ocs.l, lateral 
muscle of the oesophagus ; V.ann, pulsating circular vessel ; Md.dr, stomach- 
glands ; V v-l vein connecting the inferior and lateral blood-vessels ; Md, stomach ; 
Bm, muscles 'of the hairs; G, brain; fl.o, ciliated organ; qm, transverse muscle. 



MOLLUSCS. 137 

The most highly organized eyes in Annelids appear to 
be those of the Alciopidse, which have been described 
by Krohn,* de Quatrefages,t and especially by Greef $ 
and Graber.§ The Alciopidee are small 
sea-worms ; they live principally in |E 
the open sea, and, like many other J 
pelagic animals, are extremely trans- ijL 
parent. It is, indeed, often difficult ^ 
to see more of them than the two jf 
very large eyes, red or orange, and a ^ 
pair of dark violet dots (the seg- ^jg 
mental organs) on each ring. j& 

The principal parts of their eyes are ^ 1*7 % 
— (1) the outer integument, the whole |r '% $ 
of which is so transparent that it needs % |f J? 
scarcely any modification ; (2) the so- ^%^ %. 
called " eye-skin," as to the true ^% 

nature of which there is still much f 

difference of opinion; (3) the lens; (4) # 

the "corpus ciliare ; " (5) the vitreous 
humor; and (6) the retina, which 
again is composed of four layers — (a) 
the rods; (6) pigment layer; (c) \ 

granular layer ; (d) fibrous layer. Fig: fll ._ Alclope (after 

In Mollusca the eyes are variously de Q uatrefa s es > 
situated ; being, for instance, either placed on the pos- 
terior tentacles ; or between the feelers, as in the fresh- 
water species ; or on a short stalk at the side of the 

* "Zool. und Anat. Bemerk. iiber die Alciopeden," Wieqmann's 
Arch., 1845. 

" Etudes s. 1. typ. Inf. de l'emb. des Anfieles," Ann. Sri. Nat, 1850. 

t "Unt. iiber die Alciopiden," Nova Acta Acad. Leo}). Carol, 
vol. xxxix. 11, 1876. 

§ Arch, fiir Mic. Anat., 1880. 



138 



MOLLUSCS. 



feelers, as in the Prosobranchiata ; or on the back. In 
some cases they are deeply sunk, even into the brain. 




Fig. 92. — Perpendicular section through the eye-pit of a limpet (Patella) ; after 
Carriere. 1, Epithelial cells ; 2, retina cells , 3, vitreous body. 

The mussels are generally deficient in eyes ; and 
some which are, as larra, provided with an eye, lose 
their eves when mature. 




Fig. 93. — Eye of Trochus magus (after Hilger) * Gl, Vitreous body ; No, nerve. 

In the limpet (Patella),* on the outer side of the 
tentacles, where the eyes are situated in more highly 
organized species, are certain spots, which may be 

* "Fraisse. Ueber Molluskenaugen," Zeit. fur Wfcs. Zool, 1881. 
t w Beit, zur Kennt. der Gastropodenaugen," Gegenbaur's Morph. 
Jahrbuch. 1885. 



MOLLUSCS. 



139 



regarded as a very rudimentary organ for the per- 
ception of light. The skin is thrown into a pit, within 
which the epithelial cells are elongated and pigmented. 

In the sea-ear (Haliotis), and in Trochus (Fig. 93), 
the arrangement is similar, but the depression is 
deeper, the mouth is very much restricted, and the 
interior is filled by a vitreous body. 

In Murex (Fig. 94) the eye is still further developed, 
and is entirely closed in, a lens beiug present. 




Fig. 94.— Eye of Murex brandaris (after Hilger). L, Lens; 61, vitreous body; 

No, nerve. 

In the snail (Helix) the eye is still more highly 
organized. It consists of a cornea, which lies imme- 
diately below the skin ; a lens, behind which is the 
retina, consisting of three layers, (1) the rods, (2) a 
cellular layer, (3) a fibrous layer. This, indeed, appears 



140 



CUTTLE-FISH. 



to be a very general arrangement in the Mollusca. 
The power of sight given by such an eye can be but 
small. Indeed, it is probable that it does little more 




Fig. 95. — Eye of Helix pomatia (after Simroth).* ct. Cuticle ; a, epithelium ; b, cornea ; 
c, envelope of the eye ; d, cellular layer ; e, fibrils of the optic nerve ; /, feeler 
cell ; na, nerve of the tentacle ; no, optic nerve. 

than distinguish degrees of light. According to Lespes, 
a Cyclostoma only perceives the shadow of a hand at a 
distance of five inches, and a Paluclina of eight. 

It is interesting that, as Lankester first showed ,f the 
eye of Mollusca, in its gradual development, passes 
through the stages which we find are the permanent 
conditions in Patella and Haliotis, commencing as a 
depression, which grows deeper and deeper, and 
gradually closes over. 

Even in the Nautilus the cornea leaves an opening, 

* Simroth, "Ueber die Sinneswerkzeuge uns. einh. Weichthiere," 
Zeit. fur Wiss. ZooU 1876. 

f " Obs. on the Dev. of Cephalopoda," Quarterly Journal of Micro- 
scopical Science, 1875. 



COMPOUND EYES IN MOLLUSCS. 141 

through which the water has free access to the interior 
of the eye. 

In the higher cuttle-fishes (Cephalopoda) the eye is 
very complex, and the optic ganglion is in some cases 
the largest part of the brain ; but, while we find the 
same parts, as, for instance, in Helix, though in a higher 
state of development, there does not seem sufficient 
reason to regard the two organs as homologous, but 
it appears possible that the eye of the cuttle-fish had 
an independent origin. 

Certain bivalves (Lamellibranchiata) possess bright 
spots round the edge of the mantle, or on the siphon, 
which some naturalists maintain to be eyes, while 
others deny them this character, leaving their true 
function, however, undecided. . . 

But though there is much doubt in some cases, there 
are other eye-spots which are certainly true eyes. Of 
these there are two distinct types — those of Spondylus, 
Pecten, etc., on the one hand ; of Area, Pectunculus, etc., 
on the other. The latter present several features of the 
compound insect's eye. This was first noticed by Will,* 
and they have since been more fully described by 
Carrieref and Patten. $ They are composed (Fig. 96) 
of large conical cells with the points turned inwards. 
Pigment is deposited in the periphery of the cells. 
The outer surface is arched, and forms a biconvex lens. 
These cells pass gradually into those of the ordinary 
epithelium. 

It will be most convenient to consider the mode in 
which these compound eyes act when we come to 

* "Ueber die Augen der Bivalven," Frorieps Notizen, 1814. 

t "Die Sehorgane der Thiere," 1885. 

X " Eyes of Molluscs and Arthropods," Mitt Zool. Stat Neapel, 1886. 



142 AKCA — SPONDYLUS. 

consider those of insects, where they are more highly 
developed. 

The eyes of Pecten and Sponclylus are, again, formed 
on a totally different plan. 

It has been already observed that there is an 




Fig. 96. — Perpendicular section through an eye of Area Xoce (after Carriere). 1, 
Epithelium of the edge of the man le ; 2, cells of vision; 3, lens ; 4, 5, connective 
tissue ; 6, section of one of the cells. 

essential difference between the typical vertebrate and 
the typical invertebrate eye; in that while in the 
former, the optic nerve (Fig. 77) penetrates the retina 
and then spreads out on the anterior surface, so that 
tiie "rods" point away from the light; in the normal 
invertebrate eye, on the contrary, the nerve spreads 
out on the back of the retina, so that the rods point 
towards the light. Krohn,* however, made the remark- 
able discovery that in the genus Pecten the rods, like 
those of the vertebrates, are turned away from the light. 
In this case, however, the optic nerve does not enter 
the retina directly from behind, but runs round it and 
passes, so to say, over the lip of the cup. 

Here, then, we get a remarkable approach to the 
vertebrate eye ; but the similarity is still greater in 

* Muller's Arch., 1840. See also Hensen, " Ueber das Auge einiger 
Laniellibranchiaten." Zeit. fiir Wiss. Zool., 1805. 



PECTEN. 143 

Oncliidinm (a genus of slugs, widely spread over the 
Southern Hemisphere), in which Semper has shown * 
that the nerve actually pierces the retina as in verte- 




Fig. 97.— Diagram of eye of Pecten (after Hickson). a, Cornea ; b, transparent base- 
ment membrane supporting the epithelial cells of cornea; c, the pigmented 
epithelium ; d, the lining epithelium of the mantle ; e, the lens ; /, the ligament 
supporting the lens ; g, the retina ; h, the tapetum ; k, the pigment ; wi, the 
retinal nerve ; n, complementary nerve. 

brates. That this distinctive character should thus 
reappear in so distant a group is very interesting, and it 
is also remarkable that Onchidium possesses two kinds of 
eyes : some on the head, which are constructed on the 
same type as those of other molluscs ; while the peculiar 
eyes just mentioned are scattered over the back, and 
their nerves arise, not from the cephalic, but from the 
visceral ganglion. Moreover, they differ in number, 
not only in the different species, some having one hun- 
dred, some as few as twelve, and others none at all, 
but even in different individuals of the same species. 
Indeed, they are continually growing and being re- 
absorbed. But while thus resembling a simple verte- 
brate eye, the dorsal eyes of Onchidium have a totally 

* " Ueber Schnecken Augen am TVirbelthier typus," Arch, fur Mic. 
Anal, 1877. 



144 ONCHIDIILU 

different development, arising, except the nerve, entirely 
from the integument ; on the contrary, in the vertebrate 
eye, while the cornea and lens are formed from the 
skin, the retina is an outgrowth from the brain. 

Semper does not suppose that the Onchidia perceive 
any actual image with their dorsal eyes, and thinks that 
they are merely able to distinguish differences in the 
amount of light. 

They are shore-living molluscs, and are preyed on 
by small fishes belonging to the genus Perophthalrnus, 
which has the curious habit of leaving the water and 
walking about on the sand in search of food. The 
back of the Onchidium contains a number of glands, 
each opening by a minute pore; and Semper suggests 
that, when warned by the shadow of the fish, the little 
slugs eject a shower of spray, drive off their enemy, 
and save themselves. This is not quite so far-fetched 
as might at first sight appear, for we know that there 
are many other animals, the sepia, many ants, the 
bombardier and other beetles, etc., which defend them- 
selves in a similar manner. 

It seems difficult to understand why the Onchidia 
should be endowed with so many eyes. The irrelative 
repetition of organs meets us, however, continually in 
the lower animals. Moreover, in the present case 
Semper has thrown out a plausible suggestion. The 
organs of touch (see ante, p. 14) curiously resemble 
eyes in structure, and a very slight change might 
make them capable of perceiving light. It is possible, 
then, that some of them may undergo a change of 
function, and that this may throw some light on the 
variability in number. 

In the Chitonidaa, where dorsal eyes have recently 



SENSE-OKGANS OF CHITON. 



145 



been discovered by Moseley,* they are even more 
numerous. Chiton itself, indeed, has none; but in 
Schizochiton there are 300, and in Corephium more 




Fig. 98. Schematic representation of the soft and some of the hard parts in a shell of 
a Chiton ( Acanthopleura), as seen in a section vertical to the surface, and with the 
margin of the shell lying in the direction of the left side of the drawing, a, 
Conical termination of sense-organ ; b, b', ends of nerve ; c, nerve ; /, calcareous 
cornea ; g, lens ; h, iris ; k, pigmented capsule of eye ; m, body of sense-organ cut 
across ; w, nerve of eye ; p, nerve of sense-organ ; r, rods of retina. 

than ten thousand. As in Onchidium, they probably 
arose as modifications of the organs of touch, and are 
supplied by the same nerves. They possess (1) a 
cornea, (2) a perfectly transparent and strongly biconvex 
lens, and (3) the retina, which presents a layer of short 
but well-defined rods. It is interesting that they point 
towards the light, and not, as in Onchidium, away 
from it. 

* " On the Presence of Eyes in Shells of certain ChitonidsB," 
Quarterly Journal of Microscopal Science, 1885. 



CHAPTEE VII, 

THE OBGANS OF VISION IN INSECTS AND CEUSTACEA. 

I Now pass on to the eyes of insects. In most species 
of this group there are two distinct kinds: the large 
compound eyes, which are situated one on each side 
of the head; and the ocelli, or small eyes, of which 
there are generally three, arranged in a triangle, 
between the other two. 

Speaking roughly, the ocelli of insects may be said 
to see as our eyes do ; that is to say, the lens throws 
on the retina an image, which is perceived by the fine 
terminations of the optic nerve. One type of such an 
eye in a young water-beetle (Dytiscus) is shown in 
Fig. 84, p. 131. This illustrates the mode of develop- 
ment of an ocellus, which has been already referred to 
{ante, p. 131). 

The structure of fully formed ocelli is shown by 
Fig. 99. In details, indeed, they present many dif- 
ferences, and it is remarkable that in some species this 
is the case even with those of the same individual ; for 
instance, in those of one of our large spiders, Epeira 
diadema (Fig. 99). 

In this case the eye B would receive more light, 
and the image, therefore, would be brighter; but, on 



OCELLI. 



147 



the other hand, the image would be pictured in greater 
detail by the eye A. 




Ct. Hp 



Fig. 99.— Long peel ion through the front {A) and hinder (B) dorsal eyes of Epefra 
diadem a (after Grenadier). A, Anterior eye; #, posterior eye; Hp, hypoderm ; 
Ct, cuticle; ct, boundary membrane ; K, nuclei of the cells of the retina; M, mus- 
cular fibres ; 31, M l , cross sections of ditto ; St, rods ; Pg, P\ pigment cells ; 
L, lens , Gk\ vitreous body ; Kt, crystalline cones ; Rt, retina ; Nop, optic nerve. 

Speaking generally, an ocellus may be regarded as 
consisting of — 

1. A lens, forming part of the general body covering. 

2. A layer of transparent cells. 

3. A retina, or second layer of deeper lying cells, 
each of which bears a rod in front, while their inner 
ends pass into the filaments of the optic nerve. 

4. The pigment. 

From the convexity of the lens it would have a 
short focus, and the comparatively small number of 
rods would give but a very imperfect image, except 
of very near objects. 

But though these eyes agree so far with ours, there 
is an essential difference between them. It will be at 



148 COMPOUND EYES. 

once seen that the pigment is differently placed, being 
in front of the rods, while in the vertebrate eye it is 
behind them. Again, the position of the rods them- 
selves is reversed in the two cases. 

Passing on to the compound eye, Fig. 100 gives a 
section of the eye of a cockchafer (Melolontha), after 
Strauss-Durckheim. The separate facets of such an 



WM 




Fig. 100.— Section through the eye of a cockchafer (Melolontha) ; after Strauss- 
Diirckheim. 

eye act themselves as lenses, and give a very perfect 
image. 

As regards the number of facets, Leeuwenhoek calcu- 
lated that there were 3180 facets in the compound eye 
of a beetle which, however, he does not name. In the 
house-fly (Musca) there are about 4,000 ; in the gadfly 
(CEstrus), 7,000; in the goat moth (Cossus), 11,000; 
in the death's-head moth (Sphinx atropos), 12,000 ; 
in a butterfly (Papilio), 17,000 ; in a dragon-fly 
(iEschna), 20,000 ; in a small beetle (Mordella), as 
many as 25,000. 



STRUCTURE OF THE COMPOUND EYE. 



149 



The size of the facets seems to bear some relation to 
the size of the insect, but even in the smallest species 
none have been observed less than 2o\ro °^ an ^ nc ^ ^ n 
diameter. Butterflies, which fly in the clay, have the 
facets smaller than those of moths, which are generally 
evening insects. 

The facets are in most cases similar, six-sided, and 




Fig. 101. — Section through the eye of a fly (after Hickson). b.m, Basilar membrane ; 
c, cuticle; cop, epioptic ganglion; n.c, nuclei; n.c.s., nerve-cell sheath; X.f, 
decussating nerve-fibres ; op, optic ganglion ; pc, pseudocone ; pg, pigment cells ; 
p.op, perioptic ganglion; ?*, retinula ; Eh., rhabdom ; T, trachea; t.a., terminal 
anastomosis ; Tt, trachea ; ti, tracheal vesicle. 

very regular. In locusts, however, they vary a good 
deal both in form and size. In some flies (Diptera) 
and dragon-flies (Libellulidse) those in the upper part 
of the eye are larger than the lower ones, and the 
junction of the two often forms a well-marked, curved 
line. 



150 



CORNEA— CRYSTALLINE CONES. 



The wonderful complexity is well shown in the pre- 
ceding figure, which represents a section through the 
eye of a fly, after Hickson.* 

In illustration of the finer structure, I may take the 
eye of the bee (Apis) (Fig. 102), as described and 
figured by Grenacher in his beautiful 
work.f Fig. 102, the general accuracy 
of which has been confirmed recently 
by Dr. Hickson, represents two of the 
elements of the faceted eye. 

The structure of the eyes varies 
considerably in different groups. They 
may be said to consist of the following 
principal parts : — 

1. The cornea (Lf, Fig. 102). 

2. The crystalline cones (KJc), of 
which there is one immediately behind 
each facet. The development of the 
crystalline cone has been carefully 
studied by Claparede. It consists of 
from four to sixteen original, but com- 
pletely combined segments, secreted 
by cells which lie immediately behind 
each facet, but of which, when the eye 
is completely developed, only the 

nuclei, known as Semper's nuclei (n\ finally remain. 

3. Next comes the retinula (rl), which stands in 
more or less intimate connection with the pointed inner 
end of the crystalline cone. It is generally composed 
of seven, but sometimes of as few as four, or as many 

* " The Eye and Optic Tract of Insects," Quarterly Journal of 
Microscopical Science, 1885. 
t "Untersuchungen iiber das Sekorgan der Artkropoden." 1879. 




Fig. 102 —Two sepa- 
rate elements of the 
faceted eye of a bee 
(after Grenacher). 
Lf, Cornea ; n, nu- 
cleus of Semper ; 
Kk, crystalline cone ; 
Pg, Pg\ pigment 
cells , Rl, retinula ; 
Rm, rhabdom. 



RETINULA— PIGMENT. 151 

as eight, originally separate, but closely combined cells. 
They converge on the optic lobe, and form an outer 
nucleated sheath, enclosing a strongly refractive, 
generally quadrangular, rod (the rhabdom, Rm), the 
relation of which to the filaments of the optic nerve 
is not yet well understood. 

4. The pigment (Pg). 

Between each separate eyelet (ommateum, or omma- 
tidium, as it is termed by Hickson), is — at least, in 
some insects — a long, tubular, thin-walled trachea. 
These are difficult to see in prepared specimens, but 
have been mentioned by several observers. They were 
first, I think, figured by Leydig,* and more recently 
by Hickson. 

Finally, the eye is bounded by a basilar membrane, 
which is perforated by two sets of apertures, a series of 
larger ones for the passage of the tracheal vessels, and 
of smaller ones for the nerve-fibrils. 

The crystalline cone is not, however, always present, 
and Grenadier divides the compound eyes of insects 
into three types : acone eyes, in which the crystalline 
cone is not present, but is represented throughout life 
by distinct cells ; pseudocone eyes, in which there is a 
special conical and transparent medium ; and, lastly, 
eucone eyes, with true crystalline cones." f 

* " Zum feineren Bau der Insekten," Midler's Arch, fur Anat. u. 
Phys., 1855. 

f Acone eyes ocear in Nematocera (gnats), Heraiptera (bugs), For- 
ficula (earwigs), and those Coleoptera (beetles), which have less than 
five tarsal joints. Pseudocone eyes occur in the true flies (Muscidse). 
Eucone eyes prevail among other insects : Lepidoptera, Hymenoptera, 
Neuroptera, Orthoptera, Cicadidse, the Coleoptera with five tarsal 
segments, and among Diptera the single genus Corethra, which, more- 
over, is remarkable as possessing compound eyes, even in the larva 
and pupa, 



152 



DIFFEKENT FORMS OF EYES. 



The last form differs principally from the two first 
in that the elements which constitute the crystalline 
cone and the retinula have become completely coalesced 
and solidified. The differences are, no doubt, im- 
portant, but I need not enter into them at length here. 

Even the eucone eyes differ considerably, as may be 
seen from the following figures, representing (Fig. 103) 
an eyelet from the eye of a cockroach (Periplaneta), and 
(Fig. 104) one from that of a cockchafer (Melolontha), 
both taken from Grenadier. 



V 




U.. : 




AtW 



J rV 



t2 



Fig. 103. — Eyelet of cockroach (after 
Grenadier). If Cornea ; kk, crys- 
talline cone ; pg', pigment cell ; rl, 
retinula ; rm, rkabdoni. 



Fig. 104.— Eyelet of cockchafer 
(after Grenadier). If, Cor- 
nea; kJc, crystalline cone; 
P9* VQ\ pigment cells ; rl, 
retinula ; rl', rhabdom. 



With some few exceptions (Corethra, Libellula, etc.), 
the larvae of insects do not possess faceted eyes; indeed, 
as a general rule their powers of vision are very limited, 
or they are altogether blind. Most caterpillars have 



STKUCTURE OF THE OPTIC LOBES. 153 

on each side of the head five or six eye-spots, contain- 
ing each a crystalline body, but, as we shall presently 
see, they can probably do little more than distinguish 
between light and darkness. 

I do not propose to attempt to give here any detailed 
account of the structure of the insect brain, but I must 
say a few words on the subject. Between the brain 
proper and the eye itself there are, in, for instance, the 
blow-fly (Musca vomitoria), three distinct ganglionic 
swellings, which Hickson, a copy of whose beautiful 
figure I have given (Fig. 101), terms the " opticon " 
(op), epiopticon (cop), and periopticon (p.op). It will 
be seen that the nerve-fibrils do not pass in a direct 
course, but actually decussate, or cross from one side to 
the other, three times, once between each two ganglionic 
swellings. The optic lobes of the two sides are also con- 
nected by a fibrous- bundle. The structure of the three 
nervous swellings is also very complex. It consists of a 
fine granular matrix, traversed by a meshwork of very 
minute fibrillse, and, at least in the periopticon, is col- 
lected into a series of cylindrical masses. It is entirely 
beyond our present range of knowledge to explain the 
origin or purpose of these complex arrangements, 
though we cannot doubt that they do serve important 
functions. It is remarkable that these arrangements, 
though apparently very constant in individual species 
and genera, differ greatly in different groups of insects ; 
for instance, Hickson asserts that in the water-scorpion 
(Nepa), there is no decussation, and Carriere makes the 
same statement as regards Libellula; but it seems 
very extraordinary that this arrangement should be 
present in some insect eyes, and absent in others 
formed apparently on so nearly the same plan. 



154 KELATIONS OF OCELLUS AND EYE. 

On the Eelation of the Eye to the Ocellus. 

In considering the relation of the eye to the ocellus, 
it is obvious that we cannot regard either as derived 
from the other. They are, as G-renacher says, " sisters/ 5 
and derived from a common origin. 

The ocellus consists of a single lens in front of a 
larger or smaller number of visual rods. The com- 
pound eye consists of a number of facets, each in front 
of a single rod ; which is produced by from four to 
sixteen cells : in some cases each cell at first produces 
a separate rod, and these then subsequently coalesce 
more or less completely. Starting, then, from a simple 
form of eye consisting of a lens and a nerve-fibre, 
which would be capable of perceiving light, but would 
give no picture of the external world, we should 
arrive at the compound eye by bringing together a 
number of such eye-spots, and increasing the number 
of lenses, while the separate cells beneath each com- 
bined to form a single cone and rod ; while, on the 
other hand, by increasing the size of the lens, and 
multiplying the nervous elements behind it, we should 
obtain the ocellus of an insect, or the typical eyes of 
a vertebrate animal. 

There is, indeed, no need to suppose that these two 
eyes are derived from a common origin. We know 
that, while very similar eyes occur in distant groups of 
animals, on the other hand nearly allied species often 
differ greatly in the structure of their eyes ; that, 
indeed, eyes of very different types often occur even in 
the same animal, so that we have strong reasons for 
assuming that they had an independent and separate 
origin. 



OCELLI OF SPIDERS— MYRIAPODS. 155 

The spiders have simple ocelli only, the higher 
Crustacea compound eyes only, while many of the 
lower Crustacea and of the great class of the insects 
possess both eyes and ocelli. It would seem probable, 
therefore, that the ancestral stock must have possessed 
both, though not perhaps in so perfect a form as that 
which has now been attained, and that the spiders have 
lost the compound eyes, while, on the contrary, in the 
higher Crustacea the ocelli have disappeared. 

Moreover, though the ocellus of a spider at first 
sight closely resembles the eye of a Scoiopendra, the 
internal structure is, according to Grenadier, altogether 
different. In the ocellus of a spider or an insect we 
find, at a greater or less distance behind the lens, a 
retina consisting of a receptive surface, extended con- 
centrically with that of the lens, and consisting of a 
number of more or less rod-like perceptive elements so 
arranged that the light falls on their ends. 

On the contrary, in the eyes of Myriapods there is, 
he says, either a single element behind the cornea, or 
where there are many such elements, they are arranged 
with their longer axes perpendicular to the direction 
of light ; so that any separate perception of the rays 
of light coming from different points seems to be an 
impossibility. In the eye of Lithobius, behind the 
biconvex lens, he states that the cells lining what I 
may call the tube of each separate eye, terminate in 
filaments, between the free ends of which is left a narrow' 
passage, down which the light must pass to reach the 
end of the optic nerve. Such a structure is certainly 
very remarkable, and seems entirely to preclude the 
possibility of the formation of a true image. Altogether 
the account given by Grenadier, both as to the mode 



156 



EYES OF CRUSTACEA. 



of action of the eyes of the Myriapods and as to their 
internal structure, differs entirely from that of Graber. 




Fig. 105.— Leptodora byalina. 



The Eyes of Crustacea. 

The eyes of many Crustacea are highly developed. 
In the higher families (thence named Podophthalmata, 



STRUCTURE OF EYE 



157 



or stalk-eyed) they are situated on more or less 
elongated pedestals. In some of the lower forms, 
though less complex, they are very large, occupying, 
as in the curious Leptodora (Fig. 105) of our deep 
lakes, the whole front of the head ; while in Cory casus 




Fig. 106.— Eye of Mysis (after Grenadier), n, Nuclei; Lf, facets; Kh, crystalline 
cones; n', cells of the retinula ; Rl, retinula ; Rm, rhabdom ; Cp, blood-vessels; 
iV, fibres of the optic nerve; iY 1 , JV 11 , iV ul , JV 1111 , decussations of the fibres of the 
optic nerve; G, G\ G lL , G lli , ganglia; M> muscles for the movement of the 
eye-stalk ; Km\ Km 11 , nuclei. 

(Fig. 107) they extend to more than one-half of the 
whole length of the body. 

The higher Crustacea possess no ocelli. In the 
low r er species, on the contrary, a central ocellus is often 
present, especially in the young state. 



1 58 MYSIS — CORYCiEUS— COPILIA. 

In illustration of the compound eyes of Crustacea, I 
give a figure of an eye of Mysis (Fig. 106). 

In the higher Crustacea the nervous elements of 
the eye are, moreover, very complex. There are no 
less than four optic ganglia (Fig. 106), and there is 
a chiasma, or decussation of fibres (lY 1 , N 11 , Y" 111 , N- un ), 
between each. 

The eyes of lobsters and of crabs offer a curious 
difference. In the former, the crystalline cones are 
very long, and the retinuleB comparatively short ; while 
in the crabs, on the contrary, the crystalline cone is 
sbort, and the retinulse long. 

The eye of Corycseus (Fjg. 107) is very* interesting. 
It is extremely large in proportion to the size of the 




Fig. 107. — Corycaeus (after Leuckart). a, b, The eye. 

animal, extending from the front of the head to the 
beginning of the abdomen. The perceptive part of 
the eye (b) is, therefore, far removed from the lens (a). 
The eye of Corycaeus appears to represent, in fact, a 
single element of a compound eve. 

The eye of Copilia is also very remarkable, the 
retinula being, at about the end of the first third of its 
length, bent at a right angle. Here also the eye is 
ahout one-third as long as the body. 

The ocelli of Crustacea have not been much studied 
with reference to their microscopic structure. Those 



CALANELLA— LIMULUS. 



159 



of Calanella are very remarkable, and, indeed, but for 
tlieir position and the presence of pigment, would 
hardly be recognized as eyes. They are three in 
number, and together form an X-shaped body (Fig. 108), 
supplied by a large nerve {N.op.), and consisting of 
three groups of large nerve-cells, embedded in pig- 
ment. There are eight in each of the two side groups, 
and ten in the central. In form they are pear-shaped, 
with the narrow end turned towards the nerve. The 
organ contains no lens nor rods. 



Tfr— ■ 




Kop.- J — 



Fig. 108.— Eyes of Calanella Mecliterranea (after Gerstarker) Pg., pigment cells; 
N.fr., frontal nerves; Nop,, nervus opticus. The numbers show the numlx-rs 
of the cells. 

The eyes of the king crab (Limulns) have been 
described by Grenacher and by Laukester and Bourne.* 
The two lateral eyes form a polished, kidney-shaped 
protuberance on each side of the great shield. The 
outer side is smooth, but on the inner surface it is 
produced into a number of conical processes (Fig. 109), 

* " On the Eyes of Scorpio and Limulus," Quarterly Journal of 
Microscopical Science, 1883. 



160 



LDIULUS. 



each of which forms a special lens. Underneath each 
of these secondary lenses is a group of large, elongated 
pigmented cells, arranged round a central space, and 
touching the lens with their outer ends, while the 




JRtl 



Fig. 109. — Diagram of a vertical section through a portion of the lateral eve of Limulus 
polyphemus, showing some of the conical lenses, and corresponding ret inn la? (after 
Lankester and Bourne), a, Cuticle ; bb, cuticular lens ; cc, hypoderni ; En, 
retinula ; m, nerves. 

inner ones are continued into the optic nerve. These 
nerve-end cells form the " retinula," while their sides, 
which face one another, are thickened, and coalesce 
into a rod, the rhabdom, which is hollow at the end 
nearest the lens, but solid towards the nerve. The 
central eye is very different. It possesses a single 
lens, like that of an ordinary ocellus, underneath 
which is a layer of cells not differing much in appear- 
ance from those of the hypoderm, and below which 
again is another layer of large nerve-cells, which, how- 
ever, are so irregular as to suggest the idea that the 
central eye of the king crab may have partially lost its 
function. The king crab, then, so remarkable in other 
ways, is also very interesting in reference to the peculiar 



SCORPIONS— LIGHT-OKGANS OF EUPHAUSIA. 161 

structure of its eyes. These can hardly be regarded 
as homologous with the compound eyes of insects and 
Crustacea, but appear to have originated independently. 
They have, indeed, hardly anything in common, except 
that of being compound eyes. 

Lastly, I may allude to the eyes of scorpions, 
which, though very different from those of Limulus 
in appearance, in Lankester's opinion approach them 
more nearly in essential constitution than any other 
known eyes. 

Before quitting this part of my subject, 1 must 
mention the curious eye-like organs of Euphausia. 

Euphausia (Fig. 110) — a shrimp-like crustacean, be- 




Fig. 110. — Euphausia pellucida (after Sars). l.o., Luminous organ. 

longing to the same group as Mysis — and some of its 
allies, are remarkable for possessing at the base of 
some of the thoracic legs, and on the four anterior 
abdominal segments, luminous eye-like organs. They 
form small bulbs, each containing a vitreous boclv, some 
pigment, a lens, and a fan-shaped bundle of delicate 
fibres, and are very conspicuous from their beautiful 
red color and glistening lustre. 



162 



LIGHT-ORGANS OF EUPHAUSIA. 



Claas * regards them as true accessory eyes. Sai s,f 
on the contrary, considers that they have no power of 
sight, but are highly differentiated luminous organs. 
He admits that they present a deceptive resemblance 
to true eyes, but has convinced himself by observations 
of the living animal that they have no power of 
vision. 

The fibrous fascicle (Fig. Ill,/) he finds to be the 
chief light-producing part.J and the lens-like body in 
front serves, as he supposes, for a condenser, producing 
a bright flash of light, the direction of which the 
animal, by means of its muscles, is able to control. 
The anterior pair (Fig. 112, lo), which differ some- 
what in structure from the rest, are situated on the 




Fig. 111. — Luminous organ of 
Euphausia (alter Sars). f, 
Fibres ; e, lens. 




Fig. 112.— Eye-stalk of Euphausia (after 
Sars). lo, Luminous organ ; a, lower 
eye. 



eye-stalks, and appear to serve as c; bull's-eyes " to 
the true organs of vision. Sars considers that the 
luminous organs do not serve as eyes, on the grounds 

* "Ueber einige Schizopoden und niedere Malacostraceen," Zcit. 
fur Wiss. Zool, 1863. 

f "On the Schizopoda," "Challenger Reports," vol. xiii. 

X Valentine and Cunningham, in a memoir just published 
(Quarterly Journal of Microscopical Science, vol. xxviii.) deny this, and 
attribute it to the inner surface of the reflector. 



MODE OF VISION BY COMPOUND EYES. 3 63 

that the nerve which supplies them is but small ; that 
the structure is not really analogous to that of a true 
eye, and that the position would be very unsuitable, 
one of them being actually situated on the stalk of 
the compound eye. 

The question does not, however, seem to be by any 
means clearly solved, and it must, I think, be admitted 
that, with the exception of the anterior pair, if the 
position does not seem suitable for true eyes, neither 
is it that which one would expect in light-organs. 

On the Mode of Vision by Means of 
Compound Eyes. 

Johannes M tiller, in his great work on the Physiology 
of Vision,* was the first to give an intelligible explana- 
tion of the manner in which insects see with their com- 
pound eyes. According to his view (see Fig. 75), 
those rays of light only which pass directly through 
the crystalline cones, or are reflected from their sides, 
can reach the corresponding nerve-fibre. The others 
fall on and are absorbed by the pigment which separates 
the different facets. Hence each cone receives light 
only from a very small portion of the field of vision, 
and the rays so received are collected into one spot 
of light. The larger and more convex, therefore, is the 
eye, the wider will be its field of vision ; while the 
smaller and more numerous are the facets, the more 
distinct will the vision be. In fact, the picture per- 
ceived by the insect will be a mosaic, in which the 
number of points will correspond with the number of 
facets. 

* " Zur vergleichenden Physiologic des Gesichtsinnes." 



164 MULLEK'S THEORY OF MOSAIC VISION. 

This theory was at first received with much favour. 
In 1852, however, G-ottsche * attacked Mullens view, 
pointing out that each separate cornea of a compound 
eye can, and in fact does, give a separate and distinct 
image. This had, indeed, long previously been ob- 
served by Leeuwenhoek, who said, " When I removed 
the tunica cornea a little from the focus of the micro- 
scope, and placed a lighted candle at a short distance, 
so that the light of it must pass through the tunica 
cornea, I then saw through it the flame of the candle 
inverted, and not a single one, but some hundreds of 
flames appeared to me, and these so distinctly (though 
wonderfully minute) that I could discern the motion of 
trembling in each of them." f 

Of this, indeed, it is easy to satisfy one's self. It is 
only necessary to look at a candle through the cornea 
of an insect, and then slightly draw back the micro- 
scope, when a thousand small images of the candle, 
each formed by one of the lenses, will be plainly seen. 
If, then, in such cases there was a retina placed at the 
proper distance, a true image would be formed, as on 
the retina in our own eyes. This paper of Gottsche's 
threw great doubt on Midler's explanation, which, 
indeed, was, in Dors's words, " abandonnee par tout le 
monde." J 

It is one thing, however, to see that the lenses throw 
distinct pictures, but quite another to understand how 
such pictures could be received on the retina, or com- 
bined into one distinct image. 

* "Beit, zur Anat. und Phys. der Fliegen und Krebse," Mailer's 
Arch., 1852. 

t A. Van Leeuwenhoek, " Select Works," translated by S. Hoole. 

X tt De la vision chez les Arthropodes," Ar. des Set. Phys. et Nat. 
Geneva: 1861. 



IMAGES THROWN BY THE CORNEA. 165 

It must, moreover, be remembered that in our eyes 
the whole field of vision is reversed, so that different 
objects remain in the same relative position. In the 
case of insects, however, it would be the image thrown 
by each facet which would be reversed, and hence the 
general effect would be altogether false. 

We must not attach too much importance to the 
mere presence of an image. Any lens-like object, even 
a globule of fat, will give one. Moreover, as Miiller 
and Helraholtz have show 7 n, the lenses of the cornea 
would be an advantage on the theory of mosaic vision, 
by assisting to condense the rays of light on the 
termination of the nerve. 

Gottsche's observation was made on the eye of the 
blow-fly (Musca vomitoria), and, as a matter of fact, the 
fly is one of those insects which do not possess a true 
crystalline cone. It is, therefore, probable that the 
image w 7 hich he saw was that of the cornea. Moreover, 
as is shown by his figure, wdiich I give below (Fig. 113), 
he states* that the image was formed at x, while the 
retina is far away at y. He suggested, indeed, that 
the so-called optic ganglion really corresponds with 
the retina of our ow 7 n eye ; but this would not remove 

* His words are — " An der hintern Flache der Crystallkorper im 
Fliegeiiauge kehrt sich sicher das Bild urn, weil das Bild dera object 
in der Lage gleich ist, und da das Mikroskop das Object einmal 
umkehrt, so mnss hier eine doppelte TJmkehrung stattfinden, einmal 
dnrch das Mikroskop und vorher durch den parabolischen Crystall- 
korper. Entsteht nun bei x (Fig. 113) ein urngekehrtes Bild, so ist 
die Frage, wird das gauze Bild von x durch den Stiel zur Betiua 
und zur Perception bei y hingeleitet oder wirkt dieser diinne Stiel 
gleichsam wie ein Diapbragma und giebt er nur einen Theil dcs 
Bildes bei x nach y " (Guttsche, " Beit, zur Anat. und Pbys. des Auges 
der Krebse und Fliegen," Arch, fur Anat. Phys. und Wiss. Medicin., 
1852). 



166 



MOSAIC VISION. 




the difficulty, because, if any definite picture is to be 
formed, the sensitive rods, cones, or other structures 
must lie in the plane of the image, 
and this is not, in fact, the case. 

Dor suggested that the crystalline 
cones are nervous structures, and cor- 
respond to the rods of the vertebrate 
eye (Fig. 79). He admits, however, 
that, as a matter of fact, the image is 
not formed at the anterior surface of 
the crystalline cones.* 

And yet in his final summary, 
having shown that the image is formed, 
not at the anterior surface, but deep 
down in the crystalline cones, he 
expresses quite a different view, 
compares the crystalline cone to 
the vitreous body, and considers that 
the true retina is to be found in an 
envelope which surrounds the cone. 

Plateau f regards the mosaic theory 
of Muller as definitively abandoned, 
but rather seems to have had in his 
mind that of Gottsche. At least, he states that, accord- 
ing to Muller, the mosaic is formed by a number of 
partial images, each occupying the base of one of the 
elements composing the compound eye. This, how- 
ever, is not Muller's theory. 

* " La cornee avec sa convexite posterieure correspond a la cornee 
et au cristallin des vertebres, le corps cristallin (avec le soi-disant 
corps vitre') et la fibre nerveuse qui s'y attache a la couche des 
batonnets, enfm le ganglion optique a celles des couches de la retine, qui 
sont compose'es des granulations, des cellules, et des fibres nerveuses." 

t " Kech. Exp. sur la Vision des Arthropodes." Bruxelles : 1887. 



Fig. 113.— One of the 
elements of the eye 
of a fly (after 
Gottsche). ^Crys- 
talline cone ; x, posi- 
tion of the image; 
s, rod ; sc, sheath ; 
scm, outer sheath ; 
r, retina ; y, seat of 
vision. 



OBJECTIONS TO OTHER THEORIES. 167 

On the other hand, Boll,* Exner,f and Grenadier 
seem to me to have proved that the compound eyes of 
insects caunot act as ours do; that the theory which 
assumes that each facet acts as a separate eye and 
projects an image on a retina, is physically untenable. 

In the first place, there are cases — for instance, 
Forficula, Dytiscus, and Stratiomys among insects ; 
Ligia and many others among Crustacea — where the 
cornese are not sufficiently arched to give any distinct 
image. But even where an image is thrown by the 
cornea, it would be destroyed by the crystalline cone. 

In certain Crustacea the crystalline cones are 
elongated and curved ; this, which Oscar Schmidt j 
regarded as fatal to Miiller's theory, is, on the con- 
trary, as Exner has pointed out, quite compatible with 
it, but, on the contrary, cannot be reconciled with the 
theory of an image. 

There are few beetles in which the cornea give 
better images than in the firefly (Lampyris splendidula). 
On the other hand, the crystalline cones entirely 
destroy these images. If the eye is looked at through 
a microscope, and the crystalline cones are left in situ, 
the field of view appears perfectly black, with a bright 
spot of light at the end of each cone. No trace of an 
image can be any longer perceived. In fact, the 
images seen by Leeuwenhoek and G-ottsche are thrown 
by the cornea only. 

In most cases, then, it w 7 ould appear that the image 
formed by the cornea is destroyed by the crystalline 

* "Beit, zur Phys. Optik," Arch. fur Anat. Phys. und Wiss. Medicin., 
1871. 

f " Ueber das Sehen von Bewegungen und der Theorie des 
zusamniengesetzten Auges," Sitz. K. Akad. d. Wiss. Wien., 1875. 

% Ibid., 1876. 



168 POSITION OF THE IMAGE. 

cone. This does not, indeed, always occur ; but even in 
such cases the image does not coincide with the posterior 
end of the cone. Grenadier repeated the experiment 
of G-ottsche with moths. Here the crystalline cones 
are firm, and are attached to the cornea. Thus he was 
able to remove the soft parts, and to look through the 
cones and the cornea. When the microscope was 
foeussed at the inner end of the coue, a spot of light 
was visible, but no image. As the object-glass was 
moved, forward, the image gradually came into view, 
and then disappeared again. Here, then, the image is 
formed in the interior of the cone itself. Exner had 
endeavoured to make this experiment with the eye of 
Hydrophilus (the great black water-beetle), but the 
crystalline cones always came away from the cornea. 
He, however, calculated the focal length, refraction, 
etc., of the cornea, and concluded that, even if, in spite 
of the crystalline cone, an image could be formed, it 
would fall much behind the retinula. In these cases, 
then, an image is out of the question. Moreover, as 
the cone tapers to a point, there would, in fact, be no 
room for an image, which must be received on an 
appropriate surface. In many insect eyes, indeed, as in 
those of the cockchafer (Fig. 100), the crystalline cone 
is drawn out into a thread, which expands again before 
reaching the retinula. Such an arrangement seems 
fatal to any idea of an image. 

Moreover, for definite vision by the formation of an 
image, it is necessary that the eye should possess some 
power of accommodation for different distances. It is 
obvious, from Fig. 76, that no distinct vision would 
be given unless the receptive surface follows the 
line a' V c\ But the position of this surface will 



ABSENCE OF POWER OF ACCOMMODATION 169 

depend upon the distance of a b c from the lens. As 
a matter of fact, Leydfg * and Leurkart t thought they 
had discovered, between the cornea and the crystalline 
cones, certain muscular fibres which might regulate 
the distance between the two, and thus effect this 
object. Subsequent observers, however, have failed to 
detect these fibres. 

Again, it will be seen, from a glance at Fig. 76, 
that in an eye constituted like ours, on the principle 
of a camera obscuia, the retina must follow a regular 
curve. If it is brought at all too far forward, or forced 
the lea t too far back, the image is at once blurred. 
Hence, in our own case the frequent need for spectacles, 
and hence it would seem that a conical retina is a 
physical impossibility. 

Plateau, indeed, adopts J a suggestion made by 
Grenadier that the absence of any means of adaptation 
may be rendered unnecessary by the length of the 
cones, the rays coming from dL-tant objects acting on 
the anterior end, those from nearer ones at a greater or 
less depth. This, I confess, seems to me inadmissible. 
In the first place, the light must surely act immedi- 
ately it impinges on the organ of perception ; and, in 
the second, the cones are, as a general rule, abso- 
lutely transparent — the light passes unimpeded through 
them. 

Again, if insects see with their compound eyes as we 
do with ours, they must, of course, possess a retina. 
No such structure, however, has been as yet shown to 

* " Zum feineren Bau der Artliropoden," Mutter's Arch, fiir AnaL 
tmd Phys., 1855. 
t " Carcinologisches," Wiegmann's Arch., 1858. 
% "Rech. Exp. sur la vision chez les Arthropodes," 1887. 



170 ABSENCE OF RETINA. 

exist. Wagner,* indeed, observed that in some cases 
the optic nerve embraces the end of the cone, and he 
supposed that it thus forms a sort of retina, for which, 
however, its form is little suited. 

I ought also to mention that Max Schultze f con- 
sidered that he had, in some few cases — for instance, 
in Syrphus — been able to observe that the termina- 
tion of the nerve does divide into a number of fibres. 
Patten,$ more recently, has also maintained the 
existence of numerous nerve-fibrils, which, however, 
subsequent observers — for instance, Kingsley § and 
Beddard || — have been unable to discover. Even, how- 
ever, if we admit the perfect correctness of Schultze's 
observation, these cases are exceptional, and the fibres 
so few that they can hardly, I think, affect the general 
conclusion. To give anything like a distinct vision, a 
very large number would be required. 

A last objection is the extreme difficulty which 
would exist of combining so many different images 
into one idea, though it must be admitted that at first 
sight this difficulty (though to a minor degree) exists 
even in the case of simple eyes, the number of which 
varies considerably. Spiders have six to eight ; some 
aquatic larvae twelve; while the Oniscoidso (wood-lice), 
assuming that their eyes are aggregates of simple eyes, 
as Muller supposed, have as many as twenty to forty. 

* Einige Benierk. iiber den Bau der zus. Augen," Arch, fur Nat, 
1835. 

f " Unt. iiber die zus. Augen der Krebse und Insecten," 1868. 

% "Eyes of Molluscs and Arthropods," Mitth. Zool. St. Neapel, 1886. 

§ " On the Divisions of the Compound Eye," Journal of Morphology, 
1887, 

|| u On the Structure of the Eye in Cyinothoidae," Trans. Boy. Soc. 
ESrn, 1887. 



SUMMARY. 171 

These, however, take in different parts of the field of 
vision. 

The principal reasons, then, which seem to favour 
Miiller's theory of mosaic vision are as follows : — 

(1) in certain cases — for instance, in Hyperia — there 
are no lenses, and consequently there can be no image ; 

(2) the image would generally be destroyed by the 
crystalline cone ; (3) in some cases it would seem that 
the image would be formed completely behind the eye, 
while in others, again, it would be too near the cornea ; 
(4) a pointed retina seems incompatible with a clear 
image ; (5) any true projection of an image would in 
certain species be precluded by the presence of im- 
penetrable pigment, which only leaves a minute central 
passage for the light-rays ; (6) even the clearest 
image would be useless, from the absence of a suit- 
able receptive surface, since both the small number 
and mode of combination of the elements composing 
that surface seem to preclude it from receiving more 
than a single impression; (7) no system of accommoda- 
tion has yet been discovered. Finally, (8) a combina- 
tion of many thousand relatively complete eyes seems 
quite useless and incomprehensible. 

On the Power of Vision in Insects, etc. 

As regards the practical vision of insects, our know- 
ledge is still very imperfect. No one, indeed, who has 
observed them can doubt that in some the sight is 
highly developed. It is impossible, for instance, to 
watch a dragon-fly hawking over a pond, — to see the 
rapidity and accuracy of its movements, and doubt 
that it can see well. 



172 ON THE POWER OF VISION IN INSECTS. 

On the other hand, Claparecle asserts that at a 
distance of twenty feet a hive bee would be unable to 
see any object which was less than eight or nine inches 
in diameter, and even at a distance of a foot he says 
that each facet would correspond to an inch and a third. 

To determine how far a faceted eye could see, he 
takes the breadth of a facet, the radius of the eye- 
sphere, and the smallest angle of vision, and the dis- 
tance in centimetres at which the facet would cover 
a centimetre, and finds for the bee, for instance, 6 '7 
centimetres. 

He then proceeds to inquire at what distance from 
the faceted eye the image is as clear as in the human 
eye, and he thinks this would be about a millimetre, 
from which it would rapidly diminish, being only -^ at 
a centimetre, and at a metre no distant vision being 
possible; so that at a very little distance such eyes 
would be as good as useless. 

"In the human eye, for example, the distance 
between the centres of two adjacent cones is only 
x^jj mm., but in Musca the distance between adjacent 
ommatidiais jj -mm. In fact, the picture, as received 
by the nerve-end cells of the Vertebrate eye, is much 
more complete in itself than it can possibly be in any 
Arthropod eye, and consequently the latter possesses 
a much more elaborate and complete translating appa- 
ratus in its retina than the former possesses." * 

Claparede arrives at this conclusion by taking 
the average curvature of the whole eye, as b ing true 
for each part. This, however, is not the case, and 
in the central region of the eye the adjacent facets 

* S. J. Hickson, " The Eye and Optic Tract of Insects," Quarterly 
Journal of Microscopical Science, vol. xxv., new series, 1885, p. 242. 



EXPERIMENTS ON VISION OF INSECTS. 173 

make but a small angle with one another. Lowne has 
calculated that wasps, humble bees, dragon-flies, etc , 
would, at a distance of twenty feet, be able to distinguish 
objects from half an inch to an inch in diameter. Thus 
a dragon-fly would see an object twenty feet from its 
eye in the same detail that a man would perceive it at 
a distance of a hundred and sixty feet. 

Moreover, when Clapaiede* observes that bees will 
return from a considerable distance straight to the door 
of their nest, and that, linger Miiller's theory, the door 
would at such a distance be absulutely invisible, he 
forgets that the bee first probably guides itself by the 
known position of the door in relation to some tree or 
other large object, then with reference to the hive 
itself, and that it is quite unnecessary to assume that 
the door is actually seen from a distance. 

With reference to the power which insects possess 
of determining form, Plateau f has recently made some 
ingenious experiments. Suppose a room into which 
the light enters by two equal and similar orifices, and 
suppose an insect set free at the back of the room, it 
will at once fly to the light, but the two openings 
being alike it will go indifferently to either one or the 
other. That such is the case Plateau's experiments 
clearly show, and, moreover, prove that a comparatively 
small increase in the amount of lio'ht will attract 
the insect to one orifice in preference to the other. It 
occurred then to Plateau to utilize this by varying the 
form of the opening, so that the light admitted being 

* "Zur Morph. der zus. Angen bei den Arthropoden/' Zeit. fur 
Wiss. Zool, 18G0. 

f Bull, de VAcad. Boy. de Belgique, t. x., 1885; Comjptes Bendus de 
la Soc. Ent. de Belg,, 1887 ; " Keen. Exp. sur la Vision cliez les 
Arthropodes," 1887. 



174 EXPEEIMENTS ON VISION OF INSECTS 

equal, the opening on the one side should leave a clear 
passage, while that on the other should be divided by- 
bars large enough to be easily visible, and sufficiently 
close to prevent the insect from passing. 

His experiments were conducted in a room five 
metres square, lighted by two similar windows looking 
to the west. It was on the first floor, and looked out 
on to fields. Moreover, he had the glass of the windows 
slightly ground, so that, while the light penetrated, 
nothing outside could be seen. He then covered up 
the windows, leaving only two orifices, one of which 
was simple and square, while the other was divided 
by cross-bars. To secure equality of light, the latter 
was left somewhat larger than the other, and the 
equivalence of the two was determined by a Rumford's 
photometer. The insects were set free on a table at 
the back of the room, exactly between the two open- 
ings, and at a distance of four metres. He states that 
a very slight difference in the intensity of the light 
determined the flight of the insect to either one or the 
other opening; while, if the amount of light was as 
nearly as possible equal, they flew as often to the one 
as to the other. 

Omitting the cases when the light was not equal, the 
numbers were as follows: — 

Clear Trellised 
opening, opening. 

Musca vomitori a (the bluebottle) 8 ... 7 

On the other hand, they were — for 

Eristalis tenax (the bee fly) 4 ... 8 

Vanessa urticse (tortoiseshell butterfly) ... ... 1 ... 5 

13 20 

In fact, then, the insects seem to have gone more 



EXPERIMENTS ON VISION OF INSECTS. 175 

often to the trellisecl opening. M. Plateau concludes 
that insects do not distinguish differences of form, or 
can only do so very badly ("lis ne distinguent pas la 
forme des objects ou la distinguent fort mal "). 

I confess, however, that these experiments, ingenious 
as they are, do not seem to me to justify the conclu- 
sions which M. Plateau has deduced from them. 
Unless the insects had some means of measuring 
distance (of which we have no clear evidence), they 
could not tell that even the smaller orifice might not 
be quite large enough to afford them a free passage. 
The bars, moreover, would probably appear to them 
somewhat blurred. Again, they could not possibly 
tell that the bars really crossed the orifice, and if they 
were situated an inch or two further off they would 
constitute no barrier. 

I have tried some experiments, not yet enough to be 
conclusive, but which lead me to a different conclusion 
from that of M. Plateau. I trained wasps to come to 
a drop of honey placed on paper, and, when the insects 
had learned their lesson, changed the form of the paper, 
as I had previously changed the color. It certainly 
seemed to me that the insect recognized the change. 
M. Forel has also tried similar experiments, and with 
the same result. 

We know, however, as yet very little with reference 
to the actual power of vision possessed by insects. 

On the Function of Ocelli. 

Another interesting question remains. What is the 
function of the ocelli ? Why do insects have two sorts 
of eyes ? 



176 ON THE FUNCTION OF OCELLI. 

Johannes Miiller considered that the power of vision 
of ocelli "is probably confined to the perception of 
very near objects. This may be inferred partly from 
their existing principally in larvae and apterous insects, 
and partly from several observations which I have 
made relative to the position of these simple eyes. In 
the genus Empusa the head is so prolonged over the 
middle inferior eye that, in the locomotion of the 
animal, the nearest objects can only come within the 
range. In the Locusta eornuta, also, the same eye lies 
beneath the prolongation of the head. ... In the 
Orthoptera generally, also, the simple eyes are, in 
consequence of the depressed position of the head, 
directed downwards towards the surface upon which 
the insects are moving." 

From these facts, he considers himself justified in 
concluding that the simple eyes of insects are intended 
principally for myopic vision. The simple eyes bear 
a similar relation to the compound eyes, as the palpi 
to the antennae. Both the antennae and compound 
eyes are absent in the larvae of insects." * 

Lowne observes | that " the great convexity of the 
lens in the ocellus of Eristalis must give it a very 
short focus, and it is manifestly but ill adapted for 
the formation of a picture. The comparatively small 
number of rods must further render the production 
of anything like a perfect picture, even of very near 
objects, useless for purposes of vision. I strongly 
suspect that the function of the ocelli is the perception 
of the intensity and the direction of light rather than 
of vision in the ordinary acceptation of the term." 

* " Physiology of the Senses," translated by Baly. 

t "On the Modification of the Eyes of Insects," Phil. Trans., 1878. 



DIFFICULTY OF SUBJECT. 177 

Reaumur, Marcel de Serres, Duges, and Porel also 
have shown that in insects which possess both ocelli 
and compound eyes, the ocelli may be covered over 
without materially affecting the movements of the 
animal ; while, on the contrary, if the compound eyes 
are so treated, they behave just as if in the dark. For 
instance, Forel varnished over the compound eyes of 
some flies (Musca vomitoria and Lucilia csesar), and 
found that, if placed on the ground, they made no 
attempt to rise; while, if thrown in the air, they flew 
iirst in one direction and then in another, striking 
against any object that came in their way, and being 
apparently quite unable to guide themselves. They 
flew repeatedly against a wall, falling to the ground, 
and unable to alight against it, as they do so cleverly 
when they have their eyes to guide them. Finally, 
they ended by flying straight up into the air, and quite 
out of sight. It seems, indeed, to be a very general 
rule that insects of which the eyes are covered, 
whether they are totally blinded, or whether the ocelli 
are left uncovered, fly straight up into the air — a very 
curious and significant fact of which I think no 
satisfactory explanation has yet been given. 

Plateau* regards the simple eyes, or ocelli, as rudi- 
mentary organs of scarcely any use to the insect. Forel 
also states, as the result of his observations, that wasps, 
humble bees, ants, etc., find their w 7 ay both in the air 
and on the ground, almost equally well without as with 
the aid of their ocelli. 

I confess that I am not satisfied on this point. In 
such experiments great care is necessary. M. Forel's 
interesting experiments with ants, whose compound eyes 

* Bull, de VAcad. Boy. de Btlgique, t. x., 1885. 



178 EXPERIMENTS 

he had covered with opaque varnish, might almost, for 
instance, be quoted to prove the same with reference 
to the compound eyes. "Mes Camponotus aux yeux 
verms, 5 ' he says, "attaquaient et tuaient aussitot une 
Formica ftisca mise au milieu d'eux, la saisissaient 
presque aussi adroitement que ceux qui avaient lenrs 
yeux. lis demenageaient un tas de larves d'un coin 
de leur recipient a l'autre avec autant de precision 
qu' avec leurs yeux." * 

On the other hand, Forel goes so far as to say that 
if the compound eyes are covered with black varnish, 
insects cannot even perceive light (" Cela prouve 
qu'elles ne voyaient plus meme la lueur"). In fact, 
the use of the ocelli seems a great enigma, at least 
when the compound eyes are present. 

We must remember that some other Articulata — 
spiders, for instance — possess ocelli only, and they 
certainly see, though not probably very well. 

Plateau has made some ingenious observations, from 
which it appears that spiders are very short-sighted, 
and have little power of appreciating form. He found 
they were easily deceived by artificial flies of most 
inartistic construction ; and he concludes that even 
hunting spiders do not perceive their prey at a greater 
distance than ten centimetres (about four inches), and 
in most cases even less. Scorpions appeared scarcely 
to see beyond their own pincers. 

I have also made some experiments on this point 
with spiders (Lycosa saccata). In this species, which is 
very common, the female, after laying her eggs, collects 
them into a ball, which she surrounds with a silken 
envelope and carries about with her. I captured a 

* Eecueil Zool. Suisse, 1SS7. 



SHORT SIGHT OF OCELLI. 179 

female, and, after taking the bag of eggs from her, put 
her on a table. She ran about awhile, looking for her 
eggs. When she became still, I placed the ball of 
eggs gently about two inches in front of her. She 
evidently did not see it. I pushed it gradually towards 
her, but she took no notice till it nearly touched her, 
when she eagerly seized it. 

I then took it away a second time, and put it in the 
middle of the table, which was two feet four inches 
by one foot four, and had nothing else on it. The 
spider wandered about, and sometimes passed close to 
the bap: of eggs, but took no notice of it. She 

O Co ' 

wandered about for an hour and fifty minutes before 
she found it — apparently by accident. I then took it 
away again, and put it down as before, when she 
wandered about for an hour without finding it. 

The same experiment was tried with other individuals, 
and with the same results. It certainly appeared as if 
they could not see more than half an inch before them 
— in fact, scarcely further than the tips of their feet. 

I may also mention that they did not appear to 
recognize their own bags of eggs, but were equally 
happy if they were interchanged. 

On the other hand, it must be remembered that the 
sac is spun from the spinnerets, and the Lycosa had 
perhaps actually never se j n the bag of eggs. Hunting 
spiders certainly appear to perceive their prey at a 
distance of at least several inches. 

Plateau has shown, in a recent memoir, that cater- 
pillars, which possess ocelli, but no compound eyes, 
are very short-sighted, not seeing above one to two 
centimetres.* 

* "Kech. Exp. sur la Vision chez les Arthropodes." Bull, dc 
9 Acad. May. de Belgique, 1888. 



180 OCELLI OF OAVE-DWELLING SPIDERS. 

Lebert has expressed the opinion* "that in spiders 
some of their eight eyes — those which are most convex 
and brightly coloured — serve to see during daylight ; 
the others, flatter and colorless, during the dusk." 
Pavesi has observed t that in a cave-dwelling species 
(Nesticus spelunearum), which belongs to a genus in 
which the other species have eight eyes, the four 
middle eyes are atrophied. This suggests th it they 
serve specially in daylight. 

Returning for a moment to the ocelli of true insects, 
it seems almost incredible that such complex organs 
should be rudimentary or useless. Moreover, the 
evidence afforded by the genus Eciton seems difficult 
to reconcile with this theory. The species of this 
genus are hunting ants, which move about in large 
armies and attack almost all sorts of insects, whence 
they are known as driver ants, or army ants. They 
have no compound eyes, but in the place of them 
most species have a single large ocellus on each side 
of the head, while others, on the contrary, are blind. 
Now, while the former hunt in the open, and have all 
the appearance of seeing fairly well, the latter con- 
struct covered galleries, and seek their prey T in hollow 
trees and other dark localities. 

Insects with good sight generally have the crystalline 
lenses narrow and long, which involves a great loss of 
light. The ocelli are specially developed in insects, 
such as ants, bees, and wasps, which live partly in the 
open light and partly in the dark recesses of nests. 
Again, the night-flying moths all possess ocelli; while 
they are entirely absent in butterflies, with, accord- 

* " Die Spinnen der Schweiz." 

t "Sopra una nuova Specie di RagiM." 



PROBABLE FUNCTION OF OCELLI. 181 

ing to Scudder, one exception, namely, the genus 
Pamphila. 

On the whole, then, perhaps the most probable view 
is that, as regards insects, the ocelli are useful in dark 
places and for near vision.* 

Whatever the special function of ocelli may be, it 
seems clear that they must see in the same manner as 
our eyes do — that is to say, the image must be reversed. 
On the other hand, in the case of compound eyes, it 
seems probable that the vision is direct, and the diffi- 
culty of accounting for the existence in the same animal 
of two such different kinds of eyes is certainly enhanced 
by the fact that, as it would seem, the image given by 
the medial eyes is reversed, while that of the lateral 
ones is direct. 

Forel, in his last memoir, inclines to this opinion, 



CHAPTER VIII. 

OK PROBLEMATICAL ORGANS OF SENSE. 

In addition to the organs of which I have attempted 
in the preceding chapters to give some idea, and to 
those which from their structure we may suppose to 
perform analogous functions, there are others of con- 
siderable importance and complexity, which are evi- 
dently organs of some sense, but the use and purpose 
of which are still unknown. 

" It is almost impossible," says Gegenbaur,* " to 
say what is the physiological duty of a number of 
organs, which are clearly sensory, and are connected 
with the integument. These enlargements are generally 
formed by ciliated regions to which a nerve passes, 
and at which it often forms enlargements. It is 
doubtful what part of the surrounding medium acts on 
these organs, and we have to make a somewhat far- 
fetched analogy to be able to regard them as olfactory 
organs.'' 

Among the structures of which the use is still quite 
uncertain are the muciferous canals of fishes. The 
skin of fishes, indeed, contains a whole series of organs 
of whose functions we know little. As regards the 

* " Elements of Comparative Anatomy." 



MUCIFEROUS CANALS OF FISH. 183 

mueiferous canal, Schultze has suggested * that it is a 
sense-organ adapted to receive vibrations of the water 
with wave-lengths too great to be perceived as ordinary 
sounds. Beard also leans to this same view. However 
this may be, it is remarkably developed in many deep- 
sea fish. 

In some cases peculiar eye-like bodies are developed 
in connection (though not exclusively so) with the 
mueiferous canal. Leuckart,t by whom they were 
discovered, at, first considered them to be accessory 
eyes, but subsequent researches led him to modify 
this opinion, and to regard them as luminous organs. 
UssowJ has more recently maintained that they are 
eyes, and Leydig considers them as organs which 
approach very nearly to true eyes (" welche wirblichen 
sehorganen sehr nahe stehen "). Whatever doubt there 
may be whether they have any power of sight, there is 
no longer any question but that they are luminous, 
and they are especially developed in the fishes of the 
deep sea. 

These are very peculiar. The abysses of the ocean 
are quite still, and black darkness reigns. The 
pressure of the water is also very great. 

Hence the deep seas have a peculiar fauna of their 
own. Surface species could not generally bear the 
enormous pressure, and do not descend to any great 
depth. The true deep-sea forms are, however, as yet 
little known. They are but seldom seen, and when 

* "Ueber die Sinnesorgane der Seitenlinie bei Fischen und 
Amphibien," Arch, filr Mic. Anat., 1870. 

t " Ueber muthmassliche Nebenaugen bei einem Fiscbe." Bericht 
tiber die 39 Vers., Deutscher Naturforscher, Giessen, 1864. 

X " Ueber den Bau der sog. angenalmlichen Flecken einiger 
Knochenfisebe," Bull. Soc. Imp. Moscow, 1879. 
10 



184 DEEP-SEA FISH. 

obtained are generally in a bad state of preservation. 
Their tissues seem to be unusually lax, and liable to 
destruction. Moreover, in every living organism, 
besides those usually present in the digestive organs, 
the blood and other fluids contain gases in solution. 
These, of course, expand when the pressure is 
diminished, and tend to rupture the tissues. The 
circumstances under which some deep-sea fish have 
occasionally been met with on the surface bears this 
out. They are generally found to have perished while 
endeavouring to swallow some prey not much smaller, 
or even in some cases larger, than themselves. What, 
then, has happened ? During the struggle they were 
carried into an upper layer of water. Immediately 
the gases within them began to expand, and raised 
them higher; the process continued, and they were 
carried up more and more rapidly, until they reached 
the surface in a dying condition.* 

It is, however, but rarely that deep-sea fish are 
found thus floating on the surface, and our knowledge 
of them is mainly derived from the dredge, and 
especially from the specimens thus obtained during 
the voyage of the Challenger. 

In other respects, moreover, their conditions of life 
in the ocean depths are very peculiar. The light of 
the sun cannot penetrate beyond about two hundred 
fathoms; deeper than this, complete darkness prevails. 
Hence in many species the eyes have more or less 
completely disappeared. In others, on the contrary, 
they are well developed, and these may be said to be 
a light to themselves. In some species there are a 
number of luminous organs arranged within the area 

* Gunther, " Introduction to the Study of Fishes. 3 ' 



LIGHT-ORGANS. 185 

of, and in relation to, the niuciferous system ; while in 
others they are variously situated. These luminous 
organs were first mentioned by Oocco.* They have 
since been studied by Giinther, Leuckart, Ussow, 
Leydig, and Emery. Lastly, they have been carefully 
described by Giinther, Moseley, and von Lendenfeld 
in the work on "Deep-Sea Fishes," in vol. xxvii. of 
the "Challenger Reports." The deep-sea fish are 
either silvery, pink, or in many cases black, sometimes 
relieved with scarlet, and, when the luminous organs 
flash out, must present a very remarkable appearance. 
We have still much to learn as to the structure and 
functions of these organs, but there are cases in 
which their use can be surmised with some probability. 
The light is evidently under the will of the fish. It is 
easy to imagine a Photichthys (Fig. 114), swimming 




Fig. 114.— Photichthys argenteus ("Challenger Reports," vol. xxvii.). 

in the black depths of the ocean, suddenly flashing out 
light from its luminous organs, and thus bringing into 
view any prey which may be near; while, if danger 
is disclosed, the light is again at once extinguished. 
It may be observed that the largest of these organs is 
situated just under the eye, so that the fish is actually 
provided with a bull's eye lantern. In other cases 

* Nuovi Ann. dei Sci. Nut., 1838. 



186 



LIVING LAMPS. 



the light may rather serve as a defence, some having — 
as, for instance, in the genus Scopelus — a pair of large 
ones in the tail, so that " a strong ray of light shot 
forth from the stern-chaser may dazzle and frighten an 
enemy." * In other cases they probably serve as lures. 
The " sea-devil," or " angler," of our coasts has on 
its head three long, very flexible, reddish filaments, 
while all round its head are fringed appendages, closely 
resembling fronds of seaweed. The fish conceals itself 
at the bottom , in the sand or among seaweed, and 
dangles the long filaments in front of its mouth. 
Other little fishes, taking them for worms, unsuspect- 
ingly approach, and themselves fall victims. 

Several species of the same family live at great 




Fig. 115.— Ceratius bispinosus (" Challenger Reports, " vol. xxvii.). 

depths, and have very similar habits. A mere red 
filament would, however, be invisible in the dark, and 
therefore useless. They have, however, developed 
(Fig. 115) a luminous organ, a living " glow-lamp," at 

* Giinther, " Challenger Keporls," vol. xxvii. 



PROBLEMATICAL ORGANS IN LOWER ANIMALS. 187 

the end of the filament, which doubtless proves a very 
effective lure.* 

These cases, however, though very interesting, throw 
little light on the use of the muciferous system 
in ordinary fish, which, I think, still remains an 
enigma. 

In some of the lower animals, the nerves terminate 
on reaching the skin at the base of rod-like structures 
similar, in many respects, to the rods of the retina, or 
the auditory rods of the ear, and of which it is very 
difficult to say whether they are organs of touch or of 
some higher sense. 

Round the margin of the common sea-anemone is 
a circle of bright blue spots, or small bladders. If a 
section be made, there will be found a number of 
cylindrical organs, each containing a fine thread, and 
terminating in a " cnidocil (Fig. 14) ; " and, secondly, 
fibres very like nerve-threads, swelling from time to 
time with ganglionic expansions, and also terminating 
in a cnidocil. These structures, in all probability, 
serve as an organ of sense, but what impressions they 
convey it is impossible to say. 

Some jelly-fishes (Trachynemadae) have groups of 
long hairs arranged in pairs at the base of the tentacles 
(Fig. 116), which have been regarded as organs of 
touch, and it is certainly difficult to suggest any other 
function for them. They are obviously sense-hairs, 
but I see no reason for attributing to them the sense 
of touch. 

The so-called eyes of the leech, in Leydig's f opinion, 

* Gunther, " Study of Fishes." 

t "Die Augen und neue Sinnesorgane der Egel.," Beichert's Arch,, 
1861. 



188 MEDUSA — INSECTS— CKUSTACEA. 

which is confirmed by Ranke,* are also developed from 
the supposed special organs of touch. The latter are 
much more numerous, as many as sixty being developed 




Fig. 116.— Edge of a portion of the mantle of AgJaura hemistoma, with a pair of sense- 
organs (after Hertwig). v, Velum; ft, sense-organ; ro, layer of nettle cells; t, 
tentacle. 

on the head alone. They are cylindrical organs, lined 
with large nucleated refractive cells, which occupy 
nearly all the interior. A special nerve penetrates 
each, and, after passing some way up, appears to 
terminate in a free end. 

I may also allude to the very varied bristles and 
ciri hi of worms, with their great diversity of forms. 

Among Insects and Crustacea, there are a great 
number of peculiarly formed skin appendages, for 
which it is very difficult to suggest any probable 
function. 

The lower antennae of the male in Gammarus, for 
instance, bear a very peculiar slipper-shaped organ, 
situated on a short stalk : this was first mentioned by 

* " Beit, zu der Lehre. von den Uebergangs Sinnesorganen," Zeit 
fur Wiss. Zool. y 1875. 



DIFFICULTY OF PROBLEM. 



189 



Milne Edwards, and subsequently by other authors, 
especially by Leydig.* The short stalk contains a 
canal, which appears to divide into radiating branches 
on reaching the " slipper," 
which itself is marked by a 
series of rings. 

Among other problematical 
organs, I might refer to the 
remarkable pyriform sensory 
organs on the antennae of 
Pleuromma,t the appendages 
on the second thoracic leg of 
Serolis, those on the maxilli- 
peds of Eurycopa, on the me- 
tatarsus of spiders, the finger- 
shaped organ on the antennae 
of Polydesmus, the singular 
pleural eye (?) of Pleuromm^, 
and many others. 

There is every reason to 
hope that future studies will 
throw much light on these in- 
teresting structures. We may, no doubt, expect much 
from the improvement in our microscopes, the use of 
new reagents, and of mechanical appliances, such as 
the microtome ; but the ultimate atoms of which matter 
is composed are so infinitesimally minute, that it is 
difficult to foresee any manner in which we may hope 
for a final solution of these problems. 

Loschmi it, who has since been confirmed by Stoney 
and Sir W. Thomson, calculates that each of the 

* Zeit. fur Wiss. Zool," 1878. 

t Brady, " On the Copepoda of the Challenger Expedition," vol. viii. 




Fig. 117. — Sense-organ of leech 
(from Carriere, after Kanke). 
1, Epithelium ; 2, pigment ; 3, 
cells ; 4, nerve. The longer axis 
equals -4 mm. 



3 90 SIZE OF ULTIMATE ATOMS. 

ultimate atoms of matter is at most so-.ooWou °^ an 
inch in diameter. Under these circumstances, we 
cannot, it would seem, hope at present for any great 
increase of our knowledge of atoms by improvements 
in the microscope. With our present instruments we 
can perceive lines ruled on glass which are 90,01)0 °f an 
inch apart. But, owing to the properties of light itself, 
the fringes due to interference begin to produce con- 
fusion at distances of 74,000* aDC ^ ^ n ^e brightest part 
of the spectrum, at little more than 9-0,0 oo> they would 
make the obscurity more or less complete. If, indeed, 
we could use the blue rays by themselves, their waves 
being much shorter, the limit of possible visibility 
might be extended to i2o!ooo ? an d> as Helmholtz has 
suggested, this perhaps accounts for Stinde having 
actually been able to obtain a photographic image of 
lines only xoo^ow °^ an ^ nc ^ a P ar ^. This, however, 
would appear to be the limit, and it w r ould seem, 
then, that, owing to the physical characters of light, 
we can scarcely hope for any great improvement so 
far as the mere visibility of structure is concerned, 
though in other respects, no doubt, much may be 
hoped for. At the same time, Dallinger and Eoyston 
Pigott have shown that, as far as the mere presence 
of simple objects is concerned, bodies of even smaller 
dimensions can be perceived. According to the views 
of Helmholtz, the smallest particle that could be 
distinctly defined, when associated with others, is 
about -go.Wo °f an ^ n °h * n diameter. Now, it has 
been estimated that a particle of albumen of this size 
contains 125,000,000 of molecules. In the case of such 
a simple compound as water, the number would be 
no less than 8,000,000,000. Even then, if we could 



THE KANGE OF VISION AND OF HEARING. 191 

construct microscopes far more powerful than any we 
now possess, they could not enable us to obtain by 
direct vision any idea of the ultimate molecules of 
matter. The smallest sphere of organic matter which 
could be clearly defined with our most powerful micro- 
scopes may be, in reality, very complex ; may be built 
up of many millions of molecules, and it. follows that 
there may be an almost infinite number of structural 
characters in organic tissues which we can at present 
foresee no mode of examining. 

Again, it has been shown that animals hear sounds 
which are beyond the range of our hearing, and that 
they can perceive the ultra-violet rays, which are 
invisible to our eyes.* 

Now, as every ray of homogeneous light which we 
can perceive at all, appears to us as a distinct color, 
it becomes probable that these ultra-violet rays must 
make themselves apparent to the ants as a distinct and 
separate color (of which we can form no idea), but as 
different from the rest as red is from yellow, or green 
from violet. The question also arises whether white 
light to these insects would differ from our white light 
in containing this additional color. At any rate, as 
few of the colors in nature are pure, but almost all 
arise from the combination of rays of different wave- 
lengths, and as in such cases the visible resultant 
would be composed not only of the rays w ? e see, but of 
these and the ultra-violet, it would appear that the 
colors of objects and the general aspect of nature 
must present to animals a very different appearance 
from what it does to us. 

These considerations cannot but raise the reflection 
* " Ants, Bees, and Wasps." 



192 UNKNOWN SENSES. 

how different the world may — I was going to say nmst 
— appear to other animals from what it does to us. 
Sound is the sensation produced on us when the vibra- 
tions of the air strike on the drum of our ear. When 
they are few, the sound is deep ; as they increase in 
number, it becomes shriller and shriller ; but when they 
reach 40,000 in a second, they cease to be audible. 
Light is the effect produced on us when waves of light 
strike on the eye. When 400 millions of millions of 
vibrations of ether strike the retina in a second, they 
produce red, and as the number increases the color 
passes into orange, then yellow, green, blue, and violet. 
But between 40,000 vibrations in a second and 400 
millions of millions we have no organ of sense capable 
of receiving the impression. Yet between these limits 
any number of sensations may exist. We have five 
senses, and sometimes fancy that no others are possible. 
But it is obvious that we cannot measure the infinite 
by our own narrow limitations. 

Moreover, looking at the question from the other 
side, we find in animals complex organs of sense, richly 
supplied with nerves, but the function of which we are 
as yet powerless to explain. There may be fifty other 
senses as different from ours as sound is from sight ; 
and even within the boundaries of our own senses there 
may be endless sounds which we cannot hear, and 
colors, as different as red from green, of which we have 
no conception. These and a thousand other questions 
remain for solution. The familiar world which sur- 
rounds us may be a totally different place to other 
animals. To them it may be full of music which we 
cannot hear, of color which we cannot see, of sensations 
which we cannot conceive. To place stuffed birds and 



THE UNKNOWN WORLD. 193 

beasts in glass cases, to arrange insects in cabinets, 
and dried plants in drawers, is merely the drudgery 
and preliminary of study; to watch their habits, to 
understand their relations to one another, to study 
their instincts and intelligence, to ascertain their 
adaptations and their relations to the forces of nature, 
to realize what the world appears to them ; these 
constitute, as it seems to me at least, the true interest 
of natural history, and may even give us the clue to 
senses and perceptions of which at present we have no 
conception. 



CHAPTER IX. 

ON BEES AND COLORS. 

In my book on "Ants, Bees, and Wasps,"* I have 
recorded a number of observations which seemed to 
rae to prove that bees possess the power of distinguish- 
ing colors — a power implied, of course, in the now 
generally accepted views as to the origin of the colors 
of flowers, but which had not up to that time been 
proved by direct experiment. 

Amongst other experiments, I brought a bee to some 
honey which I placed on a slip of glass laid on blue 
paper, and about three feet off I placed a similar drop 
of honey on orange paper. With a drop of honey before 
ber a bee takes two or three minutes to fill herself, then 
flies away, stores up the honey, and returns for more. 
My hives were about two hundred yards from the 
window, and the bees were absent about three minutes, 
or even less; when working quietly they fly very quickly, 
and the actual journeys to and fro did not take more 
than a few seconds. After the bee had returned twice, I 
transposed the papers ; but she returned to the honey 
on the blue paper. I allowed her to continue this for 
some time, and then again transposed the papers. She 

* u Ants, Bees, and Wasps," International Scientific Series. Kegan 
Paul, Trench & Co. 



EXPERIMENTS WITH COLORED PAPERS. 195 

returned to the old spot, and was just going to alight, 
when she observed the change of color, pulled herself 
up, and without a moment's hesitation darted off to the 
blue. No one who saw her at that moment could have 
the slightest doubt about her perceiving the difference 
between the two colors. 

I also made a number of similar observations with 
red, yellow, green, and white. But I was anxious to 
carry the matter further, and ascertain, if possible 
whether they have any preference for one color over 
another, w 7 hich had been denied by M. Bonnier. To 
test this I took slips of glass of the size used for slides 
for the microscope, viz. three inches by one, and pasted 
on them slips of paper of the same size, coloured re- 
spectively blue, green, orange, red, white, and yellow. I 
then put them on a lawn, in a row, about a foot apart, 
and on each put a second slip of glass with a drop of 
honey. I also put with them a slip of plain glass with a 
similar drop of honey. I had previously trained 
a marked bee to come to the place for honey. My 
plan then was, when the bee returned and had sipped 
for about a quarter of a minute, to remove the honey, 
when she flew to another slip. This I then took away, 
when she went to a third, and so on. In this way, as 
bees generally suck for three or four minutes, I induced 
her to visit all the drops successively before returning 
to the nest. When she had gone to the nest, I trans- 
posed all the upper glasses with the honey, and also 
moved the colored glasses. Thus, as the drop of honey 
was changed each time, and also the position of the 
colored glasses, neither of these could influence the 
selection by the bee. 

In recording the results, I marked down successively 



196 EXPERIMENTS WITH COLORED PAPERS. 

the order in which the bee went to the different coloured 
glasses. For instance, in the first journey from the 
nest, as recorded below, the bee lit first on the blue, 
which accordingly I marked 1 ; when the blue was 
removed, she flew about a little, and then lit on the 
white ; when the white was removed, she settled on 
the green, and so on successively on the orange, yellow, 
plain, and red. I repeated the experiment a hundred 
times, using tw r o different hives — one in Kent and one 
in Middlesex — and spreading the observations over 
some time, so as to experiment with different bees, and 
under varied circumstances. 

I believe that the precautions taken placed the 
colors on an equal footing, and that the number of ex- 
periments is sufficient to give a fair average. More- 
over, they were spread over several days, and the daily 
totals did not differ much from one another. The 
result shows a marked preference for blue, then white, 
then successively yellow, red, green, and orange. The 
red I used was a scarlet ; pink would, I believe from 
subsequent observations, have been more popular. I 
may also observe that the honey on plain glass was 
less visited than that on any of the colors, which was 
the more significant because when I was not actually 
observing, the colors were removed, and some drops 
of honey left on plain glass, which naturally gave 
the plain glass an advantage. 

Another mode of testing the result is to take the 
number of times in which the bee went first to each 
color, for instance, in a hundred visits she came to the 
blue first thirty-one times, and last only four ■ while to 
the plain glass she came first only five times, and last 
twenty-four times. It may be worth while to add that 
I by no means expected such a result. 



DR. MULLER'S OBJECTIONS. 197 

A recent number of Kosmos contains a very courte- 
ous and complimentary notice of these observations by 
Dr. H. Miiller, which, coming from so high an authority, 
is especially gratifying. Dr. Miiller, however, criticizes 
some of the above-mentioned experiments, and remarks 
that, in order to make the test absolutely correct, the 
seven glasses should have been arranged in every 
possible order, and that this would give no less than 
5040 combinations. I did not, however, suppose that 
I had attained to mathematical accuracy, or shown the 
exact degree of preference ; all I claimed to show was 
the existence, and order, of preference, and I think 
that, as in my experiments the position of the colors 
was continually being changed, the result in this respect 
would have been substantially the same. 

Dr. Miiller also observes that when a bee has been 
accustomed to come to one place for honey, she returns 
to it, and will tend to alight there whatever the color 
may be ; and he shows, by the record of his own 
experiences, that this has a considerable influence. 
This is so. Of course, however, it applies mainly to 
bees which had been used for some time, and were 
accustomed to a particular spot. I was fully alive to 
this tendency of the bees, and neutralized it to a 
considerable extent, partly by frequently changing the 
bee, and partly by moving the glasses. While, how- 
ever, I admit that it is a factor which has to be taken 
into consideration, I do not see that it affords any 
argument against my conclusions. The tendency would 
be to weaken the effect of preference for any particular 
color, and to equalize the visits to all the glasses. This 
tendency on the part of the bees was, as my experiments 
show, overborne by the effect produced upon them 



198 REPLY TO OBJECTIONS. 

by the color. So far, then, from weakening my eon- 
elusions, the fact, so far as it goes, tends to strengthen 
them, because it shows that notwithstanding this 
tendency the blue was preferred, and the honey on 
colorless glass neglected. The legitimate conclusion 
to be drawn seems, I confess, to me, not that my mode 
of observation was faulty, but rather that the pre- 
ference of the bees for particular colors is even some- 
what greater than the numbers would indicate. 

Next, Dr. Muller objects that when disturbed from 
one drop of honey, the bees naturally would, and that 
in his experiments they actually did, fly to the next. 
As a matter of fact, however, this did not happen in 
mine, because, to avoid this source of error, when I 
removed the color I gave the bee a good shake, and so 
made her take a flight before settling down again. 

According to my experience, bees differ considerably 
in character, or, I should rather perhaps say, in humour. 
Some are much shyer and more restless than others. 
When disturbed from the first drop of honey, some are 
much longer before they settle on the next than others. 
Much also, of course, depends on how long the bee has 
been experimented on. Bees, like men, settle down to 
their work. Moreover, it is no doubt true that, ceteris 
paribus, a bee in search of honey will go to the nearest 
source. 

But, as a matter of fact, in my hundred experiments 
I had but very few cases like those quoted above from 
Dr. Muller. This arose partly from the fact that my 
bees were frequently changed, and partly because, as 
already mentioned, I took care, in removing the color, 
to startle the bee enough to make her take a little 
flight before alighting again. Dr. Muller says that in 



PREFERENCES OF BEES. 199 

his experiments, when the bee did not go to the next 
honey, it was when he shook her off too vigorously. I 
should rather say that in his observations he did not 
shake the bee off vigorously enough. The whole 
objection, however, is open to the same remark as the 
last. The bee would have a tendency, of course, like 
any one else, to go to its goal by the nearest route. 
Hence I never supposed that the figures exactly indi- 
cate the degree of preference. The very fact, however, 
that there would naturally be a tendency on the part 
of the bees to save themselves labour by going to the 
nearest honey, makes the contrast shown by my 
observations all the more striking. 

I have never alleged that it was possible, in the case 
of bees (or, for that matter, of men either), to get any 
absolute and exact measure of preference for one color 
over another. It would be easy to suggest many con- 
siderations which would prevent this. For instance, 
something would probably depend on the kind of 
flower the bee had been in the habit of visiting. A 
bee which had been sucking daisies might probably 
behave very differently from one which had been 
frequenting a blue flower. 

So far, however, as the conclusions which I ventured 
to draw are concerned, I cannot see that they are in 
any way invalidated by the objections which Dr. 
Midler has urged, which, on the other hand, as it seems 
to me, rather tend to strengthen my argument. 

I may perhaps be asked, If blue is the favourite 
color of bees, and then pink, and if bees have had so 
much to do with the origin of flowers, how is it there 
are so few blue and pink ones? 

The explanation I believe to be that all blue flowers 



200 THE COLORS OF FLOWERS. 

have descended from ancestors in which the flowers 
were red, these from others in which they were yellow, 
while originally they were all green — or, to speak more 
precisely, in which the leaves immediately surrounding 
the stamens and pistil were green ; that they have 
passed through stages of yellow, and generally if not 
always red, before becoming blue. 

It is, of course, easy to see that the possession of color 
is an advantage to flowers in rendering them more 
conspicuous, more easily seen, and less readily over- 
looked, by the insects which fertilize them ; but it is 
not quite so clear why, apart from brilliancy and 
visibility at a distance, one color should be more 
advantageous than another. These experiments how- 
ever, which show that insects have their pseference, 
throw some light on the subject. 

Where insects are beguiled into visits, as is the case 
especially with flies, they are obviously more likely to 
be deceived if the flowers not only, as is often the case, 
smell like decaying animal substance, but almost re- 
semble them in appearance. Hence many fly flowers 
not only emit a most offensive smell, but also are dingy 
yellow or red, often mottled, and very closely resemble 
in color decaying meat. 

There remains another case in which allied flowers, 
and species, moreover, which are fertilized by very much 
the same insects, are yet characterized by distinct 
colors. We have, for instance, three nearly allied 
species of dead nettle — one white {Lamium album), one 
red {Lamium wiaculatum), and one yellow {Lamium 
galeobdolon or luteum). 

Now, if we imagine the existence in a single genus 
of three separate species, similar in general habit and 



THE COLOKS OF FLOWEKS. 201 

appearance, and yet mutually infertile, it is easy to 
see that it would be an advantage to them to have 
their flowers differently colored. The three species 
of Larnium above mentioned may be growing together, 
and vet the bees, without difficulty or loss of time, can 
distinguish the species from one another, and collect 
pollen and honey without confusing them together. On 
the other hand, if they were similarly colored, the 
bees could only distinguish them with comparative 
difficulty, involving some loss of time and probably 
many mistakes. 

1 have not yet alluded especially to white flowers. 
They seem to stand in a somewhat special position. 
The general sequence, as I have suggested, is from 
green, through yellow and red, to blue. Flowers 
normally yellow seldom sport into red or blue; those 
normally red often sport into yellow, but seldom into 
blue. On the other hand, flowers of almost any color 
may sport into white. White is produced by the 
absence of color, may therefore appear at any stage, 
and will be stereotyped if for any reason it should prove 
to be an advantage.* 

* The genesis of the color is a large and interesting question. It 
may be due to various causes, and is by no means always owing to the 
presence of a different coloring matter. For instance, as Professor 
Foster Las observed to me, many species of Iris occur in blue and 
yellow forms. The yellow is largely, or wholly, produced by chroma- 
toplacts, the purple or blue to cell-sap, and if the latter is absent the 
yellow becomes apparent. 



CHAPTEE X. 

on the limits of vision of animals. 

Ants and Colors. 

I have elsewhere * recorded a series of experiments on 
ants with light of different wave-lengths, in order, if 
possible, to determine whether ants have the power of 
distinguishing colors. For this purpose I utilized the 
dislike which ants, when in their nest, have for light. 
Not unnaturally, if a nest is uncovered, they think they 
are being attacked, and hasten to carry their young 
away to a darker and, as they suppose, a safer place. 
I satisfied myself, by hundreds of experiments, that if 
I exposed to light the greater part of a nest, but left 
any of it covered over, the young would certainly be 
conveyed to the dark part. In this manner I satisfied 
myself that the various rays of the spectrum act on 
them in a different manner from that in which they 
affect us; for instance, that ants are specially sensitive 
to the violet rays. 

But I was anxious to go beyond this, and to attempt 
to determine whether, as M. Paul Bert supposed, their 
limits of vision are the same as ours. We all know that 

* M Ants, Bees, and Wasps." 



THE ULTRA-VIOLET RAYS. 203 

if a ray of white light is passed through a prism, it is 
broken up into a beautiful band of colors, known as the 
spectrum. To our eyes this spectrum, like the rainbow, 
which is, in fact, a spectrum, is bounded by red at the 
one end and violet at the other, the edge being sharply 
marked at the red end, but less abruptly at the violet 
But a ray of light contains, besides the rays visible to 
our eyes, others which are called, though not with 
absolute correctness, heat-rays and chemical rays. 
These, so far from falling within the limits of our vision, 
extend far beyond it, the heat-rays at the reel end, the 
chemical or ultra-violet rays at the violet end. 

I made a number of experiments which satisfied me 
that ants are sensitive to the ultra-violet rays, which 
lie beyond the range of our vision. I was also anxious 
to see how two colors identical to our eyes, but one 
of which transmitted and the other intercepted the 
ultra-violet rays, would affect the ants. 

Mr. Wigner was good enough to prepare for me a 
solution of iodine in bisulphide of carbon, and a second 
of indigo, carmine, and ro.-eine mixed so as to produce 
the same tint. To our eyes the two were identical both 
in color and capacity ; but of course the ultra-violet 
rays were cut off by the bisulphide-of-carbon solution, 
while they were, at least for the most part, transmitted 
by the other. I placed equal amounts in flat-sided 
glass bottles, so as to have the same depth of each 
liquid. I then laid them, as in previous experiments, 
over a nest of Formica fusca. In twenty observations 
the ants went seventeen times in all under the iodine 
and bisulphide, twice under the solution of indigo 
and carmine, while once there were some under each. 
These observations, therefore, show that the solutions. 



204 PERCEPTION OF LIGHT 

though apparently identical to us, appeared to the ants 
very different, and that, as before, they preferred to 
rest under the liquid which intercepted the ultra-violet 
rays. In two or three cases only they went under the 
other bottle ; but I ought to add that my observations 
were made in winter, when the ants were rather 
sluggish. I am disposed to think that in summer 
perhaps these exceptional cases would not have 
occurred. 

Professor G-raber, however, while admitting the 
accuracy of my observations, has attempted to prove 
that the perception of the ultra-violet rays is not a 
case of sight in the ordinary acceptation of the words, 
but is due to the general sensitiveness of the skin. 

It has long been known that some of the lower 
animals which do not possess eyes are, nevertheless, 
sensitive to light. Hoffrueister,* in his work on earth- 
worms, states that, with some exceptions, they are 
very sensitive to light. Darwin, perhaps, experimented 
with a different species (for there are many different 
kinds) ; at any rate, his specimens seemed to be less 
keenly affected, though it one was suddenly illumi- 
nated it dashed " like a rabbit into its burrow." He 
observed, however, that some individuals were more 
sensitive to light than other?, and that the same indi- 
viduals by no means always acted in the same way. 
Moreover, if they "were employed in dragging leaves 
into their burrows or in eating them, and even during 
the short intervals when they rested from their work, 
they either did not perceive the light or were regard- 
less of it."| He observes, however, that it is only the 

* " Familie der Begemvurmer," 1845. 
f Darwin's "Earthworms." 



BY THE GENERAL SURFACE OF THE SKIN. 205 

anterior extremity of the body, where the cerebral 
ganglia lie, which is affected by light, and he suggests 
that the light may pass through the skin and acts 
directly on the nervous centres. 

Lacaze-Duthiers, Haeckel, Engelmann, Graber, 
Plateau, and other naturalists have abundantly proved 
the sensitiveness to light of other eyeless animals. 

There has, indeed, long been a vague idea that blind 
people have some faint perception of light through the 
general surface of the skin. So far as I am aware 
there is not the slightest evidence or foundation for this 
belief; nor, indeed, has it been advocated by any com- 
petent authority. It seems a priori improbable that 
an animal with complex eyes should still retain a 
power which would be almost entirely useless. 

On the other hand, it is unquestionable that light 
can, and often does, act directly on the nerve termi- 
nations without the intermediate operation of any 
optical-apparatus. 

Some of them might, perhaps, be open to criticism. 
The effect of heat may not have been always sufficiently 
guarded against. Again, it is quite true that, as Plateau 
observes "Lorsque les Myriapudes chilopodes aveugles 
ou munis d'yeux, deposes sur le sol, s'introduisent avec 
empressement dans la premiere fente qu'ils rencon- 
trent, cet acte n'est pas determine par le seul besoin de 
fuir la lumiere, ces animaux cherchent en meme temps 
un milieu humide et avec lequel la plus grande partie 
de la surface de leur corps soit en contact direct." * 
But though this is no doubt true, and though, perhaps, 
the moisture may be some help, still, whatever be their 

* Plateau, " Rech. sur la perception de la lumiere par les Myriapodes 
aveugles," Jour, de VAnatomie, etc., T. xxii. 1S86. 



206 PERCEPTION OF LIGHT 

object, we can hardly doubt that the absence of light is 
the principal guide. 

Professor Graber,* in his interesting memoir on 
this subject confirms the observations on ants and 
Daphnias, in which I showed that they are sensitive to 
the ultra-violet rays, by similar observations on earth- 
worms, newts, etc. It is interesting, moreover, that the 
species examined by him showed themselves, like the 
ants, specially sensitive to the blue, violet, and ultra- 
violet rays. Graber, however, states that he differs 
from me inasmuch as I attribute the sensitiveness to 
the ultra-violet rays exclusively to vision ; — that it is 
" aussehliesslich durch die Augen vermittelt." I am 
not, however, of that opinion as a general expression, 
though I believe it to be true of ants, where the 
opacity of the chitine renders it unlikely that the light 
could be perceived except by the medium of the eyes 
or ocelli. 

Graber has shown in earthworms and newts, and 
Plateau t in certain Myriapods, that these animals 
perceive the difference between light and darkness by 
the general surface of the skin. But more than this. 
Graber seems to have demonstrated that earthworms 
and newts distinguish not only between light of differ- 
ent intensity, but also between rays of different wave- 
lengths, preferring red to blue or green, and green to 
blue. He found, moreover, as I did, that they are 
sensitive to the ultra-violet ray.*. Earthworms, of 
course, have no eyes; but, thinking that the light might 

* "Fundamental Versuche liber die Helligkeits und Farben Em- 
pfindlichkeit augenloser und geblendeter Thiere," Sitz. Kais. Akad. 
d. Wiss. Wien: 1883. 

t Journ. de V Anatomie et de la Phydologie, 1886. 



BY THE GENERAL SURFACE OF THE SKIN. 207 

act directly on the cephalic ganglia, Graber decapi- 
tated a certain number, and found that the light still 
acted on them in the same manner, though the differ- 
ences were not so marked. He also covered over the 
eyes of newts, and found that the same held good with 
them. 

Hence he concludes that the general surface of the 
skin is sensitive to light. These results are certainly 
curious and interesting, but even if we admit the 
absolute correctness of his deductions, I do not see that 
they are in opposition to those at which I had arrived. 
My main conclusions were that ants, Daphnias, etc., 
were able to perceive light of different wave-lengths, 
and that their eyes were sensitive to the ultra-violet 
rays much beyond our limits of vision. His observa- 
tions do not in any way controvert these deductions; 
indeed, the argument by which he endeavours to prove 
that the effect is due to true light, and not to warmth, 
presupposes that sensations which can be felt by the 
general surface of the skin, would be still more vividly 
perceived by the special organs of vision. 

In connection with this subject, I may add that I do 
not at all doubt the sensitiveness to light of eyeless 
animals. In experimenting on this subject, I have 
always found that though the blind woodlice (Platy- 
arthrus), which live with the ants, have no eyes, yet if 
part of the nest be uncovered and' part kept dark, 
they soon find their way into the shaded part. It is, 
however, easy to imagine that in unpigmented animals, 
whose skins are more or less semi-transparent, the 
light might act directly on the nprvous system, even 
though it could not produce anything which could be 
called vision. 
11 



208 EXPERIMENTS WITH HOODWINKED ANTS. 

Forel, in some recent experiments, varnished over 
the eyes of fifteen ants (Camponotus ligniperdus) and 
put them with fifteen others, which were left in their 
normal condition, in a flat box with a glass top and 
divided in the middle into two halves by a cardboard 
division, which, however, left room enough underneath 
for the ants to pass freely from one half to the other. 
After some -other experiments, in the course of which 
one of the varnished ants was accidentally killed, at 
1 p.m. all the varnished ants and thirteen of the un- 
varnished were in the right half of the box, and two 
unvarnished in the left. He then placed over the 
whole box two flat bottles containing water to inter- 
cept heat-rays — over the right half a piece of cobalt 
(violet) glass ; and over the left, a flat bottle containing 
a solution of esculine, which is quite transparent, but 
cuts off the ultra-violet rays. At 1.55 the result was 
as follows : — 

Under the esculine. Under the cobalt. 

5 varnished. 9 varnished. 

13 normal. 2 normal. 

The esculine and cobalt were then transposed. At 
2.3 the position was — 

Under the cobalt. Under the esculine. 

4 varnished. 13 varnished. 

3 normal. 12 normal. 

The esculine and cobalt were again transposed, and 
one normal ant was accidentally wounded and removed. 
At 3.8— 

Under the esculine. Under the cobalt. 

3 varnished. 12 varnished. 

11 normal. 3 normal. 



EXPERIMENTS WITH HOODWINKED ANTS. 209 

The esculine and cobalt were once more transposed, 
and at 3.13 there were — ■ 

Under the cobalt. Under the esculine. 

3 varnished. 11 varnished, 

1 normal. 13 normal. 

Thus the number of ants which followed the esculine 
and moved from one half of the box to the other at 
each transposition of the esculine and cobalt, was as 
follows : — 





Varnished. 


Normal. 


First change ... 


5 ... 


... 11 


Second „ 


1 ... 


... 10 


Third „ 


... 


9 


Fourth „ 


... 


... 10 



6 40 

And the number remaining under the cobalt and 
esculine respectively was — 





Under the 
Varnisned. 


cobalt. 

Normal. 


Under the esculine. 
Varnished. Normal 


First experiment . . . 
Second „ 
Third „ 
Fourth „ 


... 9 
... 4 
... 12 
... 3 


2 ... 
3 

3 ... 
1 ... 


5 13 
... 10 12 

3 11 
... 12 13 



28 9 30 49 

These experiments clearly showed that, while the 
normal ants moved from side to side so as to be under 
the esculine and consequently protected from the ultra- 
violet rays, those in which the eyes had been varnished 
remained unaffected by the transposition of the esculine 
and the cobalt, showing that the difference was per- 
ceived, not by the general surface of the skin, but by 
the eyes, and that when these were covered the ants 
were unaffected by the change. 



210 CONFIRMATION OF MY EXPERIMENTS ON ANTS. 

It might be suggested that possibly the ants had 
been injured or stupefied by the varnishing. M. Forel 
accordingly, on the following day at 8 a.m., placed over 
one half of the box a layer of water six centimetres 
deep, and on the other a piece of red glass, which, 
while intercepting some of the liizht, allows almost all 
the heat to pass through. At 9.25 there were — 

Under the red glass. Under the layer of water. 

3 varnished. 11 varnished. 

12 normal. 2 normal. 

Here, it seems that the ants which could see pre- 
ferred the shade, even though they were rather too 
warm ; while the hoodwinked ants went under the 
cool water. 

This indicated that the varnished ants remained 
sensitive to heat, though not to light. Indeed, Forel 
states that they were just as lively, just as sensitive to 
currents of air, as the normal ants.* 

These experiments, then, entirely confirm those I 
had made. " C'est une confirmation entiere," says 
Forel, "des resultats de Lubbock f " and he sums up as 
follows: — The ants " paraissent percevoir l'ultra- violet 
principalement avec leurs yeux, c'est-a-dire qu'elles le 
voient, car lorsque leurs yeux sont vernis elles s'y 
montrent presque inlifferentes ; elles ne rengissent 
alors nettement qu'a une lumiere solaire directe ou 
moins forte. Les experiences ci-clessus semblent in- 
diquer que les sensations dermatoptiques sont plus 
faibles chez les fourmis que chez les animaux etudies 
par Graber." 

From these and other experiments M. Forel comes 

* Log. cit, p. 167. t Ibid., p. 174. 



EXPERIMENTS WITH DAPHNIAS. 



211 



to the same conclusion as I did, that the ants perceive 
the ultra-violet rays with their eyes, and not as suggested 
by Graber, by the skin generally. It is very gratifying 
that my experiments and conclusions should thus be 
entirely confirmed by an observer so careful and so 
experienced as M. Forel. 




Fig. 118. — Daphnia pulex. a, Antenna?; T), brain; e, eye; h, heart; m, muscle of 
eye; n, nerve of eye; o, ovary; oZ, olfactory organ; s, stomach ; y, three eggs 
deposited in the space between the back and the shell. 



Experiments with Daphnias. 

The late M. Paul Bert made some very interesting 
experiments on a small fresh-water crustacean belong- 



212 DAPHNIAS AND COLORS. 

ing to the genus Daplmia (Fig. 118), from which he 
concludes that they perceive all the colors known to us, 
being, however, especially sensitive to the yellow and 
green, and that their limits of vision are the same as ours. 

Nay, he even goes further than this, and feels justi- 
fied in concluding, from the experience of two species 
— Man and Daphnia — that the limits of vision would 
be the same in all cases. 

His words are — 

1. " Tous les animaux voient les rayons spectraux 
que nous voyous." 

2. " lis ne voient aucun de ceux que nous ne voyons 
pas." 

3. " Dans l'etendue de la region visible, les differences 
entre les } ouvoirs eclairants des differents rayons 
colores sont les memes pour eux et pour nous." 

He also adds, "Puisque les limites de visibilite 
semblent etre les memes pour les animaux et pour 
nous, ne trouvons-nous pas la une raison de plus pour 
supposer que le role des milieux de l'oeil est tout a fait 
seconclaire, et que la visibilite tient a l'impression- 
nabilite de l'appareil nerveux lui-meme ? " 

These generalizations would seem to rest on a very 
narrow foundation. I have already attempted to show 
that the conclusion does not appear to hold good in the 
case of ants ; and I determined, therefore, to make some 
experiments myself on Daphnias, the results of which 
are here embodied.* 

Professor Dewar was kind enough to arrange for me, at 
the Koyal Institution, a spectrum, which, by means of a 
mirror, was thrown on to the floor. I then placed some 

* These observations were published in the Journal of the Linnean 
Society for 1881. 



PREFERENCE FOR YELLOWISH GREEN. 213 

Daphnias in a shallow wooden trough fourteen inches 
by four inches, and divided by cross partitions of ^lass 
into divisions, so that I could isolate the parts illumi- 
nated by the different coloured rays. The two ends of 
the trough extended somewhat beyond the visible 
spectrum. I then placed fifty specimens of Daphnia 
pidex in the trough, removing the glass partitions so 
that they could circulate freely from one end of the 
trough to the other. Then, after scattering them 
equally through the water, I exposed them to the 
light for ten minutes, after which I inserted the glass 
partitions, and then counted the Daphnias in each 
division. The results were as follows : — 

Number of Daphnias. 





Beyond 

the red. 


In the 
red and 
yellow. 


In the 

greenish yellow 

and green. 


In the 
blue. 


In the 
violet. 


Beyond 

the 
violet. 


Obs.l 


... 


20 


28 


2 








„ 2 


... 1 


21 


25 


3 








* 3 


... 2 


21 


24 


3 








» * 


... 1 


19 


29 


1 








„ 5 


... 


20 


27 


3 









4 101 133 12 

I may add that the blue and violet divisions were 

naturally longer than the red and green. 

May 25. — Tried again the same arrangement, but 

separating the yellow, and giving the Daphnias the 

choice between red, yellow, green, blue, violet, and 

dark :— • 





Dark. 


Violet. 


Blue. 


Green. 


Yellow. 


Red. 


Exp. 1 ... 


... 





3 


39 


5 


3 


„ 2 ... 


... 


1 


2 


37 


7 


3 


„ 3 ... 


... 





4 


31 


10 


5 


v 4 - 


... 


1 


5 


30 


8 


6 


n 5 ... 


... 


1 


4 


33 


6 


6 



18 170 36 23 



214 EXPERIMENTS. 

Of course, it must be remembered that the yellow band 
is much narrower than the green. I reckoned as yellow 
a width of three-quarters of an inch, and the width of 
the green two inches. 

Again — 







Dark. 


Violet. 


Blue. 


Green. 


Yellow. 


Bed. 


Exp. 1 ... 


... 








4 


30 


6 


10 


„ 2 ... 







1 


3 


25 


8 


13 


„ 3 ... 


... 








2 


24 


9 


15 


» 4 - 




1 





3 


25 


8 


13 


n 5 ... 


... 





1 


2 


24 


7 


16 






1 


2 


14 


128 


38 


67 


Adding them to- 














gether, we 


get 


1 


5 


32 


298 


74 


90 



M. Paul Bert observes (Joe. cit.) that in his experiments 
the Daphnias followed exactly the brilliance of the 
light. It will be observed, however, that in my expe- 
riments this was not the case, as there were more 
Daphnias in proportion, as well as absolutely, in the 
green, although the yellow is the brightest portion of 
the spectrum. In fact, they follow the light up to a 
certain brightness ; but, as will be seen presently, they 
do not like direct sunshine. 

I then arranged the trough so that the yellow fell in 
the middle of one of the divisions. The result was — 

Number of Daphnias. 



Ultra- red 

and 
lower red. 


Upper edge. 

of red, 
yellow, and 
lower green. 


Greenish 

blue and 

blue. 


Violet. 


Ultra- 
violet. 


.. 8 


38 


4 








.. 9 


36 


5 








.. 8 


39 


3 









Exp. 1 ... 
„ 2 
5 , 3 ... 

25 113 12 

May 18. — In order to test the limits of vision at the 



LIMITS OF VISION OF DAPHNIAS. 215 

red end of the spectrum, I used the same arrangement 
as before, placing the trough so that the extreme 
division was in the ultra-red, and the second in the red. 
I then placed sixty Daphnias in the ultra-red. After 
five minutes' exposure, I counted them. There were in 
the — 

Red. Ultra-red, 

Exp. 1 54 ... 5 

„ 2 56 ... 4 

I now gave them four divisions to select from — dark, 
red, ultra-red, and dark again. The numbers were — 

Dark. Red. • Ultra-red Dark. 

Exp. 1 5 47 6 2 

„ 2 ... 9 41 7 3 

I then shut them off from all the colors excepting 
red, giving them only the option between red and 
ultra-red : — 

Red. Ultra-red. 

Exp. 1 „, ... ... 46 ... ... 4 

„ 2 47 ... ... 3 

„ 3 44 6 

I then left them access to a division on the other side 
of the red, which, however, I darkened by interposing a 
piece of wood. This ecabled me better to compare the 
ultra-red r^ys with a really dark space : — 

Exp. 1 

n 2 

These observations appear to indicate that their 
limits of vision at the red end of the spectrum coincide 
approximately with ours. 

I then proceeded to examine their behaviour with 
reference to the other end of the spectrum. 

In the first place, I shut them off from all the rays 



irk. 


Red. 


Ultra-red. 


4 


43 


3 


3 


45 


2 



216 PERCEPTION OF ULTRA-VIOLET RAYS 

except the bine, vio"!et, and ultra-violet. The result 

was as follows : — 

Number of Daphnias. 

Ultra-violet. Violet. Blue. Dark. 

Exp. 1 1 9 38 2 

„ 2 4 6 38 2 

„ 3 ets „, ... 2 46 2 

5 17 122 6 

This shows that they greatly prefer blue and violet to 
darkness or ultra-violet. 

I afterwards gave them only the option of ultra-violet, 
violet, and darkness : — 

Exp. 1 

„ 2 

„ 3 

» * 

,, 5 • *> ... ... 



They preferred the violet; 
more in the ultra-violet than in the dark. 

I then tried ultra-violet and dark. The width of the 
violet was two inches; and I divided the ultra-violet 
portion again into divisions each of two inches, which 
we may call ultra-violet, further ultra-violet, and still 
further ultra-violet. The results were — 

Number of Daphnias. 



Ultra-violet. 


Violet. Dark. 


8 




48 4 


6 




48 6 


,.. 12 




47 1 


,.. 15 




42 3 


... 4 




53 3 


45 




238 1J 


; but 


th 


ere were many 



Exp. 1 ... 
„ 2 ... 


Still further 
ultra-violet. 

... 

... o 


Further 
ultra-violet. 

6 

5 


Ultra-violet. 
52 
52 


Dark. 
2 
3 


* 3 ... 


... 


6 


50 


4 


„ 4 ... 
„ 5 ,.. 


... 

,.. 


4 
4 


53 
54 


3 
2 



286 14 



PERCEPTION OF ULTRA-VIOLET RAYS. 217 

In this case the preference for ultra-violet over dark 
was very marked. 

May 18. — I again tried them with the ultra-violet 
rays, using three divisions — namely, further ultra-violet, 
ultra-violet, and dark. The numbers were as follows, 
viz. under the — 



Exp. 1 

« 2 



Further 
ultra-violet. 


Ultra-violet. 


Dark. 


... 6 


50 


4 


.. 3 


55 


2 



105 



To my eye there was no perceptible difference be- 
tween the further ultra-violet and the ultra-violet 
portion ; but slightly undiffused light reached the two 
extreme divisions. It may be asked why the still 
further ultra-violet division should have been entirely 
deserted, while in each case two or three Daphnias were 
in the darkened one. This, I doubt not, was due to the 
fact that, the darkened division being next to the ultra- 
violet, one or two in each case straggled into it. 

Not satisfied with this, I tried another test. There are 
some liquids which, though transparent to the rays 
we see, are quite opaque to the ultra-violet rays. 
Bisulphide of carbon, for instance, is quite colourless 
and transparent : it looks just like water, but it entirely 
cuts off the ultra-violet rays. If, then, we place the 
trough containing Daphnias, as I had previously done 
my nest of ants, in the ultra-violet part of the spectrum, 
and then place over one half of it a flat bottle contain- 
ing water, and over the other half a similar bottle con- 
taining bisulphide of carbon, both halves will seem 
equally dark to us, but the ultra-violet rays reach one 
half of the vessel, while they are cut off from the other. 



218 PEKCEPTION OF ULTKA-ViOLET RAYS. 

To our eyes both, as I say, are equally dark, and so they 
would be to the Baphnias if their limits of vision were 
the same as ours. As a matter of fact, however, the 
Daphnias all collected in the part of the trough under 
the water, and avoided that under the bisulphide of car- 
bon, showing that this, therefore, was to them darker 
than the other. I varied the experiments in several 
ways, but always with similar results. Bichromate of 
potash is also impervious to the ultra-violet rays, and 
had the same effect. 

Not satisfied with this, I tried to test it in another 
way. 

I took a cell, in which I placed a layer of five-per- 
cent, solution of chromate of potash less than an eighth 
of an inch in depth, and which, though almost colourless 
to our eyes, completely cut off the ultra-violet rays. I 
then turned my trough at right angles, so that 1 could 
cover one side of the ultra-violet portion of the spectrum 
with the chromate and leave the other exposed. The 
numbers were as follows : — 

Side of the ultra- 
violet covered with Side 
chromate of potash, uncovered. Dark. 

Exp. 1 .. 5 ... 55 ... 

I now covered up the other side. 

Exp. 2 3 ... 57 ... 

Again covered up the same side as at first. 

Exp. 3 4 ... 56 ... 

Again covered up the other side. 

Exp. 4 ... 3 ... 57 ... 

May 19. — I again tried the same arrangement, re- 
ducing the chromate of potash to a mere film, which, 



Under the fill 
chroniate of p<. 


m of 

,tash. 


Under the 
water. 


... 8 


... 


52 


... 4 


... 


56 


... 10 




50 


... 7 


• •• 


53 



OBJECTIONS OF M. MEREJKOWSKY. 219 

however, still cut off the ultra-violet rays. I then placed 
it, as before, over one half of the ultra-violet portion of 
the spectrum ; and over the other half I placed a similar 
cell containing water. Between each experiment I 
reversed the position of the two cells. The numbers 
were — 



Exp. 1 

, 2 ... 

is 3 ... 

» 4 ... 

Evidently, then, even a film of chromate of potash 
exercises a very considerable influence; and, indeed, I 
doubt not that, if a longer time had been allowed, the 
difference would have been even greater. 

It seems clear, therefore, that a five-per cent, solution 
of chromate of potash only one-eighth of an inch in 
thickness, which cuts off the ultra-violet rays, though 
absolutely transparent to our eyes, is by no means so to 
the Daphnias. 

These observations seem to prove, though I differ 
with great reluctance from so eminent an authority as 
M. Paul Bert, that the limits of vision of Daphnias do 
not, at the violet end of the spectrum, coincide with 
ours, but that the Daphnia, like the ant, is affected by 
the ultra-violet rays. 

Since these observations were published, M. Merej- 
kowski has experimented on the subject, and come 
to the conclusion that the Daphnias are attracted 
wherever there is most light, that they are conscious 
only of the intensity of the light, and that they have no 
power of distinguishing colors. It is no doubt true 
that in ordinary diffused daylight the Daphnias generally 



220 



DAPHNIAS SUPPOSED TO PERCEIVE 



congregate wherever the light is strongest. Their eyes 
are, however, so delicate that one would naturally expect, 
a priori, that there would be a limit to this ; and, in 
fact, direct sunshine is somewhat too strong for their 
comfort. 

For instance, I took a porcelain trough, seven and a 
half inches long, two and a half broad, and one deep, and 
put in it some water containing fifty Daphnias. One 
half I exposed to direct sunlight, and the other I shaded, 
counting the Daphnias from time to time, and trans- 
posing the exposed and shaded halves. The numbers 
w ere as follows: — 







In the sun. 


In the shade 


At 10.40 a.m 


4 


46 


n 12.50 „ 




.. 8 


42 


„ i.io „ 




7 


43 


„ 1.35 „ 




... 7 


43 


„ 1.50 „ 




.. 4 


46 


,, Z D „ ... 




3 


47 


„ 2.40 „ ... . 




.. 4 


46 


» 3.0 „ 




.. 5 


45 


n 4.0 „ ... 




7 


43 


„ 4 30 „ ... 




... 4 


46 



53 



447 



This seems clearly to show that they avoid the full 
sunlight. 

I believe, then, that in some of my previous experi- 
ments the yellow light was too brilliant for them ; and 
the following experiments seem to show that, when 
sufficiently diffused, they prefer yellow to white light. 

M. Merejkowsky, however, denies to the Crustacea 
any sense of color whatever. His experiments were 
made with larvae of Balanus and with a marine cope- 
pod, Bias longiremis. These, if I understand him 
correctly, have given identical results. He considers 



BRIGHTNESS, BUT NOT COLOR. 221 

that they perceive all the luminous rays, and can dis- 
tinguish very slight differences of intensity ; but that 
they do not distinguish between different colors. He 
sums up his observations as follows : — 

" II resulte de ces experiences que ce qui agit sur les 
Crustaces, ce n'est point la qualite de la lumiere, c'est 
exclusivement sa quantite. Antrement dit, les Crus- 
taces inferieurs ont la perception de toute onde lumi- 
nense et de toutes les differences, raeme ties legeres, dans 
son intensite ; mais ils ne sont point capabies de dis- 
tinguer la nature cles ondes, de differentes couleurs. Ils 
distinguent ties bien l'intensite des vibrations etherees, 
leur amplititde, mais point leur nombre. Ilya done, 
dans le mode de perception de la lumiere, une grande 
difference entre les Crustaces inferieurs et 1'Homme, et 
meme entre eux et les Fourmis ; tandis que nous 
voyons les differentes couleurs et leurs differentes 
intensites, les Crustaces inferieurs ne voient qu'une 
seule couleur dans ses differentes variations d'intensite. 
Nous percevons des couleurs comme couleurs ; ils ne 
les perpoient que comme lumiere." * 

It is by no means easy to decide such a question 
absolutely ; but the subject is of much interest, and 
accordingly I made some further experiments, as it did 
not seem to me that those of M. Merejkowsky bore out 
the conclusion he has deduced from them. 

Professor Dewar most kindly arranged the apparatus 
for me again. He prepared a normal diffraction-spec- 
trum, produced by a Eutherfurd grating with 17,000 
lines to the inch ; the spectrum of the first order was 
thrown on the trough. In this case the distribution of 

* M. C. Merejkowsky, " Les Crustaces inferieurs distinguent -ils lea 
couleurs ? " 



222 FURTHER EXPERIMENTS. 

luminous intensity has been shown to be uniform on 
each side of the line having the mean wave-length, i.e. 
a little above the line D in the yellowish green of the 
spectrum. 

I then took a long shallow trough in which were 
a number of Daphnias, and placed it so that the 
centre of the trough was at the brightest part of 
the spectrum, a little, however, if anything, towards 
the green end. After scattering the Daphnias equably 
I left them for five minutes, and then put a piece of 
blackened cardboard over the brightest part. After 
five minutes more, there were at the green end, 410; 
in the dark, 14 ; at the red end, 76. Here the two 
ends of the trough were equally illuminated ; but 
the preference for the green over the red side was very 
marked. 

I then took five porcelain vessels, seven and a half 
inches long, two and a half broad, and one deep, and 
in each I put water containing fifty Daphnias. One 
half of the water I left uncovered ; the other half I 
covered respectively with an opaque porcelain plate, a 
solution of aurine (bright yellow), of chlorate of copper 
(bright green), a piece of red glass, and a piece of blue 
glass. Every half-hour I counted the Daphnias in 
each half of every vessel, and then transposed the 
coverings, so that the half which had been covered was 
left exposed, and vice versa. I also changed the Daph- 
nias from time to time. 

Here, then, in each case the Daphnias had a choice 
between two kinds of light. It seemed to me that this 
would be a crucial test, because in every case the 
colored media act by cutting off certain rays. Thus 
the aurine owes its vellow color to the fact that it cuts 



FURTHER EXPERIMENTS. 223 

off the violet and blue rays. The light beneath it con- 
tains no more yellow rays than elsewhere; but those 
rays produce the impression of yellow, because the 
yellow is not neutralized by the violet and blue. In 
each case, therefore, there was less light in the covered 
than in the uncovered part. 

After every five experiments I added up the number 
of the Daphnias; and the following table gives twenty 
such totals, each containing the result of five observa- 
tions, making in all one hundred. 

My reason for adding one vessel in which one half 
had an opaque cover was to meet the objection that 
possibly the light might have been too strong for the 
Daphnias ; so that when they went under the sheltered 
part they did so, not for color, but for shade. I was 
not very sanguine as to the result of this arrangement, 
because I had expected that the preference of the 
Daphnias for light would overcome their attachment to 
yellow. 

The numbers were as in the following table (p. 224\ 

The result was very marked. The first two columns 
show the usual preference for light. If the covered 
half had been quite dark, no doubt the difference in 
numbers would have been greater; but a good deal of 
light found its way into the covered half. Still the 
result clearly shows that the Daphnias preferred the 
lighter half. The numbers were 2043 in the dark to 
2952 in the light; and it will be seen that the preference 
for the light was shown, though in different degrees, in 
almost every series. 

The result in the blue gives, I think, no evidence as 
to color-sense. The numbers were respectively 204b* 
against 2954, and were therefore practically the same 



224 



EVIDENCE THAT DAPHNIAS. 



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PERCEIVE DIFFERENCES IN COLOR. 22o 

as in the preceding set. Since, however, a certain 
quantity of light was transmitted through the blue, the 
result may indicate a want of sensitiveness to the blue 
rays. 

In the red the numbers were 1928 as against 3072. 

As regards the yellow, the results were very different, 
the numbers being, under the yellow, 3096 ; in the 
uncovered part, 1904. Here, therefore, we see a very 
distinct preference, all the more remarkable because 
the amount of light was really less than in the un- 
covered part. 

In the green the numbers were much more equal, 
namely, 2406 against 2594. Here also the love for green 
neutralized the preference for light. I do not, however, 
wish for the moment to draw any conclusion from these 
last figures, though I give them for what they are worth. 
The coloured medium was, I believe, somewhat too 
opaque. With a more transparent green, as will be 
seen subsequently, the result would have been very 
different. 

At any rate, the above observations seemed to show a 
marked preference for yellow. Still, I thought it might 
be objected that, though the Daphnias obviously pre- 
ferred the uncovered to the shaded half of the vessel, 
and the yellow to the uncovered half of the vessel, 
perhaps in the former the uncovered water was rather 
too bright, and in the latter the shaded part was rather 
too dark, and that after all the yellow was chosen, not 
because it was yellow, but because it hit off the happy 
medium of intensity. The suggestion is very improb- 
able, because the observations were made on several 
successive, and very different, days, and at very 
different hours. I also thought that the green was 



226 EVIDENCE THAT DAPHNIAS 

perhaps too dark ; I took, therefore, a lighter tint, and 
rearranged my little apparatus as follows: — 

I placed (March 26) fifty Daphnias in a trough (1), 
covering over one half of it with a pale green, and 
another fifty in a trough (2) half of which was covered 
with, yellow (aurine). On one side was a similar trough 
(3), one end of which was shaded by a porcelain plate ; 
and on the other side a fourth trough (4), one end of 
which had a little, though but little, extra light thrown 
on it by means of a mirror. As before, I counted the 
Daphnias from time to time, and turned the troughs 
round. All four were in a light room, but not actually 
in direct sunshine. Thus, then, in one trough I had 
half the water in somewhat green light; in the second 
trough, half the water in yellow light; in the third, 
one half was exposed and the other somewhat darkened ; 
while the fourth, on the contrary, gave me a contrast 
with somewhat more vivid light. If, then, the 
Daphnias went under the green and yellow glass, not 
on account of the color, but for the sake of shade, 
then in trough 3 a majority of them would have gone 
under the porcelain plate. On the other hand, if the 
porcelain plate darkened the w r ater too much, and yet 
the open water was rather too light for the Daphnias, 
then in the fourth trough they would, of course, have 
avoided the illuminated half. The results show that 
the third trough was unnecessary, still, I may as well 
give the figures ; the fourth proves that the Daphnias 
preferred a light somewhat brighter than the ordinary 
diffused light of the room. Of course, it does not follow 
that the effect of color is the same as with us. 



PERCEIVE DIFFERENCES OF COLOR. 



227 





Trough i. 


Trough 2. 


Trough 3. 


Trough 4. 




Green 

light. 


White 

light. 


Yellow 
light. 


White 
light. 


Exposed 
half. 


Darkened 
half. 


Illumi- 
nated 
half. 


Unillu- 

minated 

half. 


March 27. 
12 
12.25 ... 

12.50 ... 
1.40 ... 
2.5 ... 


35 
32 
27 
33 

26 

153 


15 
18 
23 
17 
24 

97 


33 
28 
33 
33 
42 

169 


17 
22 
17 
17 

8 

81 


35 

37 
36 
38 
35 

181 


15 
13 
14 
12 
15 

69 


28 
36 
25 
30 
26 

145 


22 
14 
25 
20 
21 

105 


2.25 ... 
3.0 ... 
3.25 ... 
5.15 ... 
540 ... 


36 

41 
31 
35 

30 

173 


14 
9 
19 
15 
20 

77 


36 
IS 
34 
2i 
35 

148 


14 
32 
16 
25 
15 

102 


26 
24 
36 
31 
32 

149 


24 
26 
14 
19 
18 

101 


35 

23 

35 

28 
27 

148 


15 

27 
15 
22 
23 

102 


March 23. 
7.30 ... 
7.50 ... 
8.10 ... 
8.35 ... 
9.5 ... 


33 
32 
34 
36 

26 

161 


17 
18 
16 
14 
24 

89 


34 
37 
33 
35 

27 

166 


16 
13 
17 
15 
23 

84 


35 

27 
29 
26 
33 

150 


15 

23 
21 
24 
17 

100 


30 
32 
30 
33 
35 

160 


20 
18 
20 
17 
15 

90 


March 29. 
9.10 ... 
9.25 ... 
9.40 ... 
9.55 ... 
10.30 ... 


36 
30 
19 
20 
30 

135 


20 
20 
31 

30 
14 

115 


25 
27 
25 
34 
34 

145 


25 
23 
25 
16 
16 

105 


29 
35 
29 
37 
20 

150 


21 
15 
21 
13 

30 

100 


32 
30 
2d 

29 
26 

146 


18 
20 
21 
21 
24 

104 


Total ... 


622 


378 


628 


372 


630 370 


599 
[ 


401 



It may be said that perhaps in the previous 
experiments the red and blue were too dark. I 
therefore took a very pale solution, and counted the 
number twenty times for the red and ten for the blue, 



228 EVIDENCE THAT DAPHNIAS 

placing the yellow in another trough, as before, for 
comparison. The preference for the yellow was as 
marked as ever. In the experiments with the red and 
yellow the numbers were respectively 

Trough 1. Trough 2. 



Under the In the Un.ler the In the 

yellow. uncovered half. red. uncovered half. 

670 330 498 502 

When, therefore, the red solution was sufficiently 
light, the Daphnias were indifferent to it. In the 
experiments with light blue the numbers were — 

Trough 1. Trough 2. Trough 3. 



Under In the Under In the Under In the 

the uncovered the uncovered the porcelean uncovered 

yellow. halt. blue. half. plate. half. 

687 313 286 714 336 664: 

One other possible objection also suggested itself to 
me. I thought it might be said that the Daphnias 
went under the yellow and the green not on account of 
any preference for yellow or green light, but on account 
of the shelter afforded by the covering. To test this, 
I covered one half of a trough over with transparent 
glass, leaving the other uncovered; but after twenty 
observations I found the number of Daphnias iu each 
half to be practically identical. The mere fact of the 
covering, therefore, made no difference. In this way I 
was able to test the preference of the Daphnias for 
various colours, and the result made it abundantly clear 
that Daphnias have the power of distinguishing between 
light of different wave-lemrths, and that they prefer 
the light which we call yellow and green. Whether it 
actually appears to them as it dees to us is, of course, 



PERCEIVE DIFFERENCES OF COLOR. 229 

another and a more difficult question — one, moreover, 
not yet solved even for the higher animals. Nor would 
I necessarily claim for them any aesthetic sense of 
beauty; it must be remembered that they feed on 
minute algae and other minute vegetables, the prevalent 
colors of which are yellow, yellowish green, and green. 
There is, therefore, nothing improbable, a priori, but 
rather the reverse, in their preference for these colors- 
It will be observed that though in these vessels the 
Daphnias made their preference unmistakable, there 
w r ere always a certain number in the least popular 
part. This is natuial, because, as the position of the 
light half was reversed every observation, the Daphnias 
had to swim across the vessel, and some naturally did 
not find their way to the favourite part. Then, again, 
in any considerable numbers of Daphnias some are 
changing, or have recently changed, their skin, and 
are, therefore, more or less inactive. Moreover, in pure 
water the desire for food must often overpower any 
preference for one colour over another. To such causes 
as these we must, I think, attribute the presence of so 
many Daphnias in the first vessel at the opaque end, and 
in the second in the uncovered part. 

Still, it was of course not impossible that the pre- 
sence, for instance, of a certain number under the red 
and blue was due to a difference of taste; that, though 
the majority preferred yellow, there might be some 
preferring blue or red. To test this I tried the follow- 
ing experiment. I placed, as before, fifty Daphnias in 
three of the vessels, covering one half of one with the 
yellow, of a second with blue, and the third with red. 
I then from time to time, at intervals of not less than 
half an hour, removed these which were in the un- 



230 EVIDENCE THAT DAPHNIAS 

covered part and replaced them with an equal number 
of fresh ones. If, then, some Daphnias preferred red or 
blue, I ought thus to eliminate the others, and gradually 
to get together fifty agreeing in this taste. This, how- 
ever, was not the case. In the first experiment, an hour 
after the Daphnias were placed in the vessels there 
were, out of 50, 41 under the yellow, 16 under the red, 
and 15 under the blue, the remaining 9, 34, and 35 
respectively being in the uncovered portions. These, 
then, I removed and replaced by others. After doing 
this five times, and thus adding 80 in the yellow division, 
187 in the red, and 209 in the blue, the numbers were 37 
under the yellow, 15 under the red, and 6 under the blue. 

In the second experiment, the numbers after the 
first hour were 32 under the yellow, 10 under the red, 
and 11 under the blue. Aftt*r five observations, during 
which 86 were added to the yellow division, 188 to the 
red, and 180 to the bine, the numbers were — under the 
yellow, 35 ; red, 11 ; blue, 15. 

In the third experiment, the numbers after half an 
hour were 40 under the yellow, 14 under the red, and 8 
under the blue. After five observations, during which 
73 were added to the yellow, 186 to the red, and 206 
to the blue, there were — under the yellow, 43 ; under 
the red, 15 ; and under the blue, 7. 

In the fourth experiment, the numbers after half an 
hour were 38 under the yellow, 15 under the red, and 
14 under the blue. After six observations, during 
which 89 were added to the yellow, 166 to the red, and 
176 to the blue, the numbers were — under the yellow, 
30 ; under the red, 19 ; and under the blue, 10. 

In the fifth experiment, the numbers after half an 
hour were 40 under the yellow, 14 under the red, and 



41 


16 


15 


37 


15 


6 


32 


10 


11 


35 


11 


15 


40 


14 


8 


43 


15 


7 


38 


15 


14 


30 


19 


10 


40 


14 


13 


38 


13 


15 



PERCEIVE DIFFERENCES OF COLOR. 231 

13 under the blue. After seven observations, during 
which 86 were added to the yellow, 263 to the red, and 
272 to the blue, the numbers were — under the yellow, 
38; under the red, 13 ; and under the blue, 15. 

Yellow. Red. Blue. 

First observation. 

At the beginning 
„ end 
Second observation. 
At the beginniog 
„ end 
Third observation. 
At the beginning 
„ end 
Fourth observation. 
At the beginning 
„ end 
Fifth observation. 

At the beginning 
„ end 

I conclude, then, that the presence of some of the 
Daphnias in the red, blue, and violet is more or less due 
to the causes above indicated, and not to any individual 
preference for those colors. 

My experiments, I think, show that, while the Daph- 
nias prefer light to darkness, there is a certain maxi- 
mum of brilliancy beyond which the li^ht becomes 
inconveniently bright to them, and that they can 
distinguish between light of different wave-lengths. 
I suppose it would be impossible to prove that they 
actually perceive colours ; but to suggest that the rays 
of various wave-lengths produce on their eyes a different 
impression from that of color, is to propose an entirely 
novel hypothesis. 

At any rate, 1 think I have shown that they do 

distinguish between rays of different wave-lengths, and 

prefer those which to our eyes appear green and yellow. 
12 



CHAPTER XI. 

ON KECOGNITTON AMONG ANTS. 

Duetng the many years that I have had ants under 
observation, I have never on any occasion seen any- 
thing like a quarrel between any two ants belonging 
to the same community. This is certainly very much 
to their credit. The experience of Huber, Forel, 
McCook, and others who have wa'ched ants, is, 
moreover, the same as mine. I have also shown* that 
they recognize one another even after a separation of 
a year and nine months. 

On the other hand, every community of ants is hostile 
to every other. I am not now speaking of ants belong- 
ing to different kinds, but of ants belonging to the same 
species. Some species, indeed, are more intolerant of 
strangers than others ; but, as regards rn'>st species of 
ants, it may be said that if an individual be taken from 
its own nest and introduced into another, even though 
belonging to the same species, it will be at once attacked 
and driven, or rather dragged, out. 

These facts, then, show that the ants of a community 
all recognize one another. But when we consider the 
immense number of ants in a nest, amounting in some 
cases to over 500,000, this is indeed a wonderful fact, 

* See " Ants, Bees, and Wasps." 



EXPERIMENTS WITH INTOXICATED ANTS. 233 

Tt may be remembered that my nests have enabled 
me to keep ants under observation for long periods, and 
that I have thus identified workers -of Lashes niger and 
Formica fusca which were at least seven years old, but 
my oldest ants have been two queens of Formica fusca, 
which I took in a nest in December, 1874. They must 
then have been nine months old, and of course may 
have been more. One of these queens, after ailing 
for some days, died on July 30, 1887. She mu-t 
then have been more than thirteen years old. I wa*? 
at first afraid that the other one might be affected by 
the death of her companion. She is, however, still 
alive (May, 1888), and, though a little stiff in the 
joints, as far as I can judge, in her usual health. 
Still, there are only a few queens in a nest, and no 
doubt the majority of the workers, at least in the 
summer and when the community is most active, are 
very young, which adds greatly to the difficulty of sup- 
posing that they are personally known to one another. 

It has been suggested that each nest has, perhaps* 
a special s'gnal or pass-word. To test this I took, as I 
have already mentioned in my book on " Ants, Bees, and 
Wasps," a number of ants, half from one nest and half 
from another, and made them very drunk, so as to be 
thoroughly insensible. I then marked them with spots 
of different colours, so as to distinguish the two lots, 
and put them on a table near where some ants belonging 
to the nest from which one half of them had been 
taken, were feeding on some honey. The table was 
surrounded by a moat containing water to prevent the 
ants from wandering away. The sober ants were rather 
puzzled; but,after examining the intoxicated individuals, 
they picked up the strangers and threw them into the 



234 EVIDENCE AGAINST THE 

ditch, while they carried their own friends into the 
nest, where no doubt they slept off the effects of the 
spirits. This experiment seemed to show that the 
recognition was not effected by means of any sign; 
but I thought the suggestion might be tested in 
another way. 

I made, therefore, the following experiment. I took a 
few specimens of Formica fusca from two different nests, 
which I will call A and B, and placed them together. 
At first they were rather shy ; but after a while they 
fraternized. After they had lived amicably together 
for three months, I put two of these ants from nest A 
into nest B ; but they were soon attacked vigorously 
and driven out of the nest. I thought it desirable to 
repeat and extend this test. Accordingly, on June 
16 I put three specimens of F. fusca from my nest 
No. 81 with the same number from nest No. 71. Then 
on September 19, one of the six having died in the 
interval, I put the two from nest 81 into nest 71, and 
the three from nest 71 into 81. They were all attacked, 
though not very quickly or vigorously, but eventually all 
five were expelled. 

Again, on September 25 I took three ants from each 
of these nests and put the six together. Then on 
March 19 following (one having died), I put the 
two from 71 into 81, and the three from 81 into 71. 
They were all attacked, so that they were evidently 
recognized as strangers ; but it seemed to me that the 
attack was less vigorous, and I could not be sure that 
they weve either kdled or driven out. In the course of 
the week three or four dead ants were brought out of 
each of the nests; but I could not feel certain that 
they weie tbose experimented with. 



POSSESSION OF A SIGN OK PASSWORD. 235 

Lastly, on April 9 I again put twelve ants, six 
from each of these nests, together, and kept them so 
till October. I then took four of those from 71, 
put three into 81 and the fourth into 71. I also took 
four of those from 81, and put three into 71, and 
the fourth back into 81 among her old friends. The 
two ants thus restored respectively to their old nests 
were as usual recognized as friends and left quite 
unmolested. As regards the other six, the results were 
as follows. The ants were introduced into the nests at 
8.15 a.m. 

Nest 71. Nest 81. 

8.45. One was being attacked, One was being attacked. 

9.15. None were „ 

9.45. Two were „ 

10.15. One was „ 

10.45. None were „ 

12.30. Two were „ 

1.30. Two were „ None were „ 

2.30. One was „ „ , ? 

I do not give these results as by any means proving 
that ants do not recognize their friends by means of 
smell. They do seem, however, at any rate, to show that 
not even six months of close companionship under pre- 
cisely similar conditions will so far assimilate the odour 
as to lead to confusion. If the recognition is due in any 
degree to this cause, the odour is therefore probably an 
hereditary characteristic. 

In the interesting memoir already cited, Forel says,* 
" Lubbock (he. cit.) a cru demontrer que les fourmis 
enlevees de leur nid a l'etat de nymphe et ecloses hors 
de chez elles etaient neanmoins reconnues par leurs 

* Becueil Zool. Suisse, 1887. 



236 EXPERIMENTS WITH ANTS REMOVED FROM THE 

compagnes lorsqu'on les leur rendait. Dans mes 
Fourmis de la Suisse, j'avais cru demontrer le contraire. 
Voici une experience que j'ai faite ces jours-ci : Le 7 
aout, je donne des nymphes de Formica pratensis pies 
d eclore a quelques Formica sanguined dans une boite. 
Le 9 aout quelques-unes eclosent. Le 11 aout, au 
matin, je prends Tune de jeunes pratensis agee de deux 
ou trois jours seuleruent et je la porte a sa fourmiliere 
natale dont elle etait sortie com me nymphe seulement 
4 jours auparavant. Elle y est fort mal recue. Ses 
nourrices d'll y a 4 jours l'empoignent qui par la tete, 
qui par le thorax, qui par les pattes en recourbant leur 
abdomen d'un air menacant. Deux d'entre elles la 
tinrent longtemps en sens inverse chacune par une 
patte en l'ecartelant. En5n cependant on fmit par la 
tolerer, comme on le fait aussi pour de si jeunes fourmis 
(encore blanc jannatre) provenant de fourmiiieres dif- 
ferentes. J'attends encore deux jours pour laisser durcir 
un peu mes nouvelles ecloses. Puis j'en reporte deux 
sur leur nid. Elles sont violemraent attaquees. L'une 
d'elles est inondee de venin, tiraillee et tuee. L'autre 
est longtemps tiraillee et mordue, mais flnalement 
laissee tranquille (toleree?). On m'objectera l'odeur 
des sanguinea qui avait vecu 4 jours avec la premiere 
et 6 jours avec les deux dernieres. A cela je repondrai 
simplement par l'experience de la page 278 a 282 de 
mes Fourmis de la Suisse, ou des F. pratensis adultes 
separees depuis deux mois de leurs compagnes pnr une 
alliance forcee avec des F. sanguinea, alliance que j'avais 
provoquee, reconnurent immediatement leurs anciennes 
compagnes et s'allierent presque sans dispute avec elles. 
Je maintiens done mon opinion : les fourmis apprennent 
a se connaitre petit a petit a partir de leur eclosion. 



NEST AS PUP;E AND SUBSEQUENTLY KESTORED. 237 

Je crois du reste que c'est au moyen de perceptions 
olfactives de contact."* 

I have, however repeated my previous observations, 
with the same results. 

At the beginning of August I brought in a nest of 
Lasius niger containing a large number of pupae. 
Some of these I placed by themselves, in charge of three 
ants belonging to the same species, but taken from a 
nest I have had under observation for rather more tban 
ten years. On August 28 I took twelve of the young 
ants, which in the mean time had emerged from the sepa- 
rated pupae, selecting some which had almost acquired 
their full colour. Four of them I placed in their old 
nest, and four in that from which their nurses were taken. 

At 4.30 in their own nest none were attacked. 

„ ,, nurses' nest one was attacked. 

5.0 „ own nest none were attacked. 

; , ? , nurses' nest all four were attacked. 

8.0 „ own nest none were attacked. 

„ „ nurses' nest three were attacked. 

The next day I took six more and marked them 
with a spot of paint as usual, and at 7.30 replaced 
them in their own nest. 

At 8.0 I found 5 quite at home ; the others I could not see, but none 

were attacked. 



„ 8.30 


rt 


5 


•)» 


n 9.0 


->y 


3 


?> 


„ 10.0 


j> 


4 


5J 


,,11.0 * 


ji 


5 


r> 


„ 12.0 


?> 


3 


» 


„ 1.0 


?? 


3 


•» 


„ 4.0 


>3 


4 


n 


„ 7.0 


» 


1 


r> 


„ 9.0 


J> 


2 


99 



* "Forel. Exp. et Rem. crit. sur les Sensations des Insectes," 
Recueil Zool. Suisse., 1887. 



238 EXPERIMENTS WITH DROWNED ANTS. 

The next morning I could only see two, but none 
were being attacked, and there were no dead ones. It 
is probable that the paint had been cleaned off the 
others, but it was not easy to find them all among so 
many. At any rate, none were being attacked, nor had 
any been killed. 

These observations, therefure, quite confirm those 
previously made, and seem to show that if pupae are 
taken from a nest, kept till they become perfect insects, 
and then replaced in the nest, they are recognized as 
friends. 

As regards the mode of recognition, Mr. McCook 
considers that it is by scent, and states that if ants are 
more or less soaked in water, they are no longer recog- 
nized by their friends, but are attacked. He mentions 
a case in which an ant fell accidentally into some 
water: " She remained in the liquid several moments, 
and crept out of it. Immediately she was seized in a 
hostile manner, first by one, and then another, then by 
a third, the two antennae and one leg were thus held. 
A fourth one assaulted the middle thorax and petiole. 
The poor little bather was thus dragged helplessly to 
and fro for a long time, and was evidently ordained to 
death. Presently I took up the struggling heap. Two 
of the assailants kept their hold, one finally dropped ; 
the other I could not tear loose, and so put the pair 
back upon the tree, leaving the doomed immersionist 
to her hard fate." 

His attention having been called to this, he noticed 
several other cases, always with t 1 e same result. I 
have not myself been able to repeat the observation 
with the same species, but with two at least of our 
native ants the results were exactly reversed. In one 



RECOGNITION AFTER A YEAR AND NINE MONTHS. 239 

case five specimens of Lasius niger fell into water and 
remained immersed for three hours. I then took them 
out and put them into a bottle to recover themselves. 
The following morning I allowed them to return. 
They were received as friends, and, though we watched 
them from 7.30 till 1.30 every hour, there was not the 
slightest sign of hostility. The nest was, moreover, 
placed in a closed box, so that if any ant were killed 
we could inevitably find the body, and no ant died. 
In this case, therefore, it is clear that the immersion 
did not prevent them from being recognized. Again, 
three specimens of Formica fusea dropped into water. 
After three hours I took them out, and, after keeping 
them by themselves for the night to recover, I put 
them back into the nest. They were unquestionably 
received as friends, without the slightest sign of 
hostility or even of doubt. I do not, however, by any 
means intend to express the opinion that smell is not 
the mode by which recognition is effected. 

It will be remembered, perhaps, that my ants (For- 
mica fusca) recognized one another after a separation 
of a year and nine months, though " after some months' 
separation they were occasionally attacked, as some of 
the ants, perhaps the young ones, did not recognize 
them. Still, they were never killed or driven out of 
the nest, so that evidently when a mistake was made 
it was soon discovered." Hence it would appear that 
there are differences in the memory of different 
species. 

In one case Forel had taken some ants from a 
large nest of Componotus, for the experiments on 
their sensibility to the ultra-violet rays, to which I 
have already referred. After his observations were 



240 SUPPOSED KECOGNITION BY SCENT. 

concluded, he returned them to the nest, some after 
eight, some after forty-one days. Those which were 
returned after eight days were at once recognized, 
while as regards those which had been forty-one days 
away from home. "On reculait de part et d'autre, se 
mena9ait des mandibnles, s'examinait a fond avec les 
antennes, se mordait nieme. Plusieurs meme allerent 
dans leur irritation jusqu' a essayer de decapiter et 
meme a decapiter quelques-unes de leurs anciennes 
compagnes et scaurs avec leurs mandibnles (c'est le 
mode de combat des Camponotus) ! Les fourmis vernies 
prirent part a ces rixes aussi bien que les non vernies ; 
je les vis meme attaquer, et elles etaient a peine 
moins adroites. Les combats ne cesserent entierement 
qu'au bout d'un on deux jours, et, a part les quelques 
vie times du premier jour, Tincident se termina par une 
alliance." 

Forel seems to entertain no doubt that the recog- 
nition is effected by a form of smell, which he terms 
" odorat au contact." He says, " Beancoup d'insectes 
out en outre une sorte d'odorat au contact que nous ne 
possedous pas et qui permet entre autres aux fourmis 
de distinguer leurs compagnes de leurs ennemies." 

His observations, however, do not favour the hy- 
pothesis that the recognition may be by smell. If 
the ants recognized their companions by any odour 
characteristic of the community, the lapse of thirty 
days could not have made any difference. Here the 
question of memory would not enter, because the per- 
ception of the odour would in both cases be continually 
before them. M. Forel is so excellent an observer, 
and has so great a knowledge of the ways of ants, 
that his opinion is entitled to great weight. It 



RECOGNITION BY MEANS OF THE ANTENNA. 241 

would be very interesting to repeat similar observations, 
for if it turn out to be the case that separations of 
comparatively few days lead, in some species, to a 
want of recognition, it would be a strong argument 
against the hypothesis that this recognition is due to 
smell. 

It certainly seems as if the recognition was effected 
to a great extent by the antennae, Not only do the 
ants cross and recross them, almost, so to say, as two 
deaf mutes conversing by their fingers ; but, as M. Forel 
has shown, if ants of different species are brought 
together after the removal of their antennae they show 
no signs of hostility. That this latter statement is 
correct I am quite content to take on M. Forel's 
authority; but it is not so conclusive as might seem 
at first sight, because in ants, as in men, " a fellow- 
feeling makes us wondrous kind." and ants when 
isolated, and especially when suffering, are much less 
pugnacious than they are under normal conditions. 



CHAPTER XII. 

ON THE INSTINCTS OF SOLITARY WASPS AND BEES. 

The hive bee and the common wasps are so familiar 
and so interesting that they have to a great extent 
diverted attention from the so-called solitary species 
of the same groups. Few, for instance, are aware that 
about 4500 species of wild bees are known, and of 
wasps 1100, of which some 170 and 16 respectively 
live in Britain. 

These insects often live in association, but do not 
form true communities. Speaking generally, we may 
say that each female constructs a cell, every species 
having its own favourite site, sometimes underground, 
sometimes in a hollow stick, in an empty snail-shell, 
or built against a wall, a stone, or the branch of a tree. 
Having completed her cell, the female stores up in it 
a sufficient supply of food, which in the case of bees 
consists of pollen and honey ; while the wasps select 
small animals, such as beetles, caterpillars, spiders, etc., 
each species generally having one kind of prey. The 
mother then lays an egg, after which she closes up 
the cell, and commences another. Having thus pro- 
vided sufficiently for her offspring, she generally takes 
no further heed of it. This is not, however, an invari- 
able rule : in the genus Bembex, for instance, the 



INSTINCT OF RENDERING VICTIMS INSENSIBLE. 243 

mother, instead of provisioning her cell once for all, 
brings food to the young grub from day to day. 

This, however, is an exceptional case, and the mode 
of life of the solitary wasps raises one of the most 
interesting questions in connection with instinct. The 
Ammophila, for instance, having built her cell, places 
in it, as food for her young, the full-grown caterpillar of 
a moth, Noctua segetum. Now, if the caterpillar were un- 
injured, it would struggle to escape and almost inevit- 
ably destroy the egg ; nor would it permit itself to be 
eaten. On the other hand, if it were killed, it would 
decay and soon become unfit for food. The wasp, however, 
avoids both horns of this dilemma. Having found her 
prey, she pierces with her sting the membrane between 
the head and the first segment of the body, thus nearly 
disabling the caterpillar, and then proceeds to inflict 
eio-ht more wounds between the following segments ; 
lastly crushing the head, and thus completely paralyzing 
her victim, but not actually killing it; so that it lies 
helpless and motionless, but, though living, let us 
hope insensible. M. Fabre, to whom we are indebted 
for a most interesting and entertaining series of essays 
on this group of insects, argues that this remarkable 
instinct cannot have been gradually acquired. 

The spots selected are, he says, exactly those 
occupied by the ganglia. No others among the in- 
numerable points which might have been chosen would 
have answered the purpose; not one wound is mis- 
placed or without effect. M. Fabre truly observes that 
chance offers no explanation.* Moreover, he unhesi- 

* In the case of other insects, such as Mutilla, Chrysis, Leucospis, 
Anthrax, etc., which do not possess the instinct of paralyzing their 
victims, the young feed on the chrysalis, which is normally without 
power of movement. 



244 OKIGIN OF INSTINCTS. 

tatingly asserts that "Si de son cote l'hymenoptere 
excelle dans son art, c'est qu'il est fait pour Fexercer ; 
c'est qu'il est done, non seulement d outils, mais encore 
de la maniere de s'en servir. Et ce don est originel, 
parfait des le debut ; le passe n'y a rien ajoute, l'avenir 
n'y ajoutera rien." * But how was it acquired ? M. 
Fabre cuts the Gordian knot. " Et tout naivement je 
me dis : Puisqu'il faut des Araignees aux Pompiles, de 
tout temps ceux-ci ont possede leur patiente astuce et 
les autres leur sotte audace. C'est pueril, si Ton veut, 
peu conforme aux visees temscendantes des theories a 
la mode; il n'y a la ni objectif ni suhjectif, ni adapta- 
tion ni differentiation, ni attavisme ni transform isme ; 
soit, mais du moins je comprends." 

"Je comprends!" M. Fabre says he understands, 
and no doubt he thinks so ; but I confess that his 
explanation seems to me to leave us just where we 
were. To my mind, I confess, it seems to me to throw 
no light whatever on the matter. M. Fabre asserts 
that the habits of these insects have been "de tout 
temps" exactly what they are now, 1 pass by the fact 
that the Hymenoptera are, geologically speaking, of 
comparatively recent appearance. But is it the case 
that habits are so invariable ? Quite the reverse. The 
cases of variation are innumerable. 

Romanes | refers to a criticism of the same nature 
by Kirby and Spence. "Why," they ask, "if instincts 
are open to modification by experience and intelligence, 
are not bees sometimes found to use mud or mortar 
instead of wax or propolis ? Show us," they say, " but 
one instance of their having substituted mud for 

* J. H. Fabre, u Nouveaux Souvenirs Entoniologiques." 
"Mental Evolution in Animals." 



HABITS NOT INVARIABLE. 245 

propolis, . . . and there could be no doubt of their 
having been guided by reason." Such eases have, how- 
ever, been observed. Andrew Knight found that his 
bees collected some wax and turpentine with which he 
had covered some decorticated trees, and used it instead 
of propolis, the manufacture of which they discontinued. 
Nay, M. Fabre has himself placed on record some cases 
of the same kind, and shown that the instincts of these 
animals are not absolutely unalterable. Thus one 
solitary wasp, Sphex flavipennis, which provisions its nest 
with small grasshoppers, when it returns to the cell, 
leaves the victim outside, and goes down for a moment 
to see that all is right. During her absence M. Fabre 
moved the grasshopper a little. Out came the Sphex, 
soon found her victim, dragged it to the mouth of the 
cell, and left it as before. Again and again M. Fabre 
moved the grasshopper, but every time the Sphex did 
exactly the same thing, until M. Fabre was tired out. 
All the insects of this colony had the same curious 
habit; but on trying the same experiment with a 
Sphex of the following year, after two or three dis- 
appointments she learned wisdom by experience, and 
carried the grasshopper directly down into the cell. 

Eumenes pomiformis builds, as already mentioned, 
a cell in the open air. If attached to a broad base, 
" O'est un dome avec goulot central, evase en embou- 
chure d'urne. Mais quand l'appui se reduit a un point, 
sur un rameau d'arbuste par exemple, le nid devient 
une capsule spherique, surmontee tonjours d'un goulo^ 
bien entendu." * 

Again, he has shown good reason for believing 
that, although the Tachytes nigra generally makes its 

* Log cit, p. ffi. 



246 CHANGE OF INSTINCTS — BEMBEX. 

own burrow and stores it with paralyzed prey for its 
own larvae to feed on, yet that, when this insect finds a 
burrow already made and stored by another Sphex, it 
takes advantage of the prize, and becomes for the 
occasion parasitic. On which Mr. Darwin has justly 
observed that he could see no difficulty in natural 
selection making an occasional habit permanent, if of 
advantage to the species, and if the insect whose nest 
and stored food are thus feloniously appropriated be 
not thus exterminated. 

The problem is certainly one of great difficulty, and 
it is with diffidence that I would suggest to M. Fabre 
certain considerations which may perhaps throw some 
light on it. Let us examine some of the other solitary 
wasps, and see whether their habits afford us any clue. 
That an animal of prey knows where its victim is 
most vulnerable, has not in itself anything unusual or 
unaccountable. 

The genus Bembex kills the insects on which its 
young are fed, and supplies the cell with a fresh 
victim from time to time. Eumenes, like Ammophila 
and Sphex, stores up the victims once for all. They 
are grievously wounded, but not altogether paralyzed. 
Here, then, we have the very condition which M. Fabre 
considers would be fatal to the tender egg of the wasp. 
But not necessarily so. The wretched caterpillars lie 
in a wriggling mass at the bottom of the cell; a clear 
space is left above them, and from the summit of the 
cell the delicate egg is suspended by a fine thread, so 
that, even if touched by a caterpillar in one of its con- 
vulsive struggles, it would simply swing away in safety. 
When the young grub is hatched, it suspends itself to 
this thread by a silken sheath, in winch it hangs head 



ODYNERUS— AMMOPHILA. 247 

downwards over its victims. Does one of them struggle ? 
quick as lightning it retreats up the sheath out of 
harm's way. 

In Oclynerus the arrangement is very similar, but 
the grub simply attaches itself to the support, and 
does not construct a tube. Moreover, while in the 
solitary bees and wasps the laying of the egg is generally 
the final operation before the closing of the cell, in 
Odvnerus, on the contrary, or at least in Odyneras 
reniformis, the egg is laid before the food is provided. 
This, perhaps, may have reference to the different con- 
dition of the victims. 

According to Marchal,* Cerceris ornata practically 
kills her victim ; moreover, she stings it not in, but 
between, the ganglia, and though the first sting is 
planted between the head and thorax, the following 
ones do not always follow the same order. 

At present the Ammophila supplies each cell with 
one large caterpillar; but was this always so? One 
species of Odvnerus deposits in each cell no less than 
twenty-four victims, another only eight. Eumenes 
Amedei regulates the number according to the sex : 
ten for the female grub, five only for the smaller male. 

Moreover, while phytophagous larvae will not gene- 
rally eat any plants but those to which they are 
accustomed, it has been proved that, as a matter of 
fact, these larvae will feed and thrive on other insects 
almost, if not quite, as well as on their natural food. 

Is it, then, impossible that in far bygone ages the 
larvae may have grown more rapidly, so that the 
victims had not time to decay; or that the ancestors 

* Marchal, " Sur Plnstinct du Cerceris ornata" Arch. d. Zool. Exper., 

1887. 



248 MODIFIABILITY OF INSTINCTS. 

of our present Ammopliilas may have fed their young 
from day to day with fresh food, as Bembex does even 
now ; that they may then have gradually brought the 
provisions at longer intervals, choosing small and 
weak victims, and laying the egg in a special part of 
the cell, as Eumenes does? that during these long- 
ages they may have gradually learnt the spots where 
their sting would be most effective, and, thus saving 
themselves the trouble of capturing a number oi 
victims, have found that it involved less labour to select 
a fine fat common caterpillar, such as that of Noctua 
segetum, and so have gradually acquired their present 
habits'? Wonderful doubtless they are; but, though 
I hint the suggestion with all deference, such a 
sequence does not seem to me to present any in- 
superable difficulty. 

This suggestion was made in the Contemporary 
Bevieiv for 1885, and I was much interested to find in 
Mr. Darwin's life that he had made a similar suggestion 
in a letter to M. Fabre. He refers to the great skill 
of the Gauchos in killing cattle, and suggests that each 
young Gaucho sees how the others do it, and with a 
very little practice learns the art. "I suppose that 
the sand-wasps originally merely killed their prey by 
stinging them in many places (see p. 129 of Fabre's 
' Souvenirs/ and p. 24.1), and that to sting a certain 
segmeut was found by far the most successful method, 
and was inherited like the tendency of a bulldog to pin 
the nose of a bull, or of a ferret to bite the cerebellum. 
It would not be a very great step in advance to prick 
the ganglion of its prey only slightly, and thus to give) 
its larvae fresh meat instead of only dried meat." * 
* "Life and Letters of Charles Darwin." 



DIFFERENCES UNDER DIFFERENT CIRCUMSTANCES. 249 

Perhaps, however, it may be asked, Why should the 
insect change its habits ? Several reasons might be sug- 
gested. The prey first selected might be exterminated, 
or at any rate dimmish in numbers, and, though each 
species as a general rule confines itself to one special 
victim, some exceptions have already been noticed. 
For instance, Sphex flavipennis habitually preys on a 
species of grasshopper, but on the banks of the Ehone 
M. Fabre found it, on the contrary, attacking a field 
cricket, whether from the absence of the grasshopper or 
not he was unable to determine. 

Take another case. M. Fabre denies* that the 
different species of Sphex can ever have been derived 
from one source. Every species now, he observes, has 
some one victim, some one insect on which it preys, to 
which it restricts itself, and which the other species do 
not attack. But " Que chassait, je vous prie, ce proto- 
type des Sphegiens ? Avait il regime varie ou regime 
uniforme ? Ne pouvant decider, examinons les deux 
cas. 

He begins by supposing that with the ancestor of the 
Sphex, " Le regime etait varie. J 'en felicite hautement 
ce premier ne des Sphex. II etait dans les meilleures 
conditions pour laisser descendance prospere." Is it 
likely then, he says, that they would have limited 
themselves to one prey, and thus have foolishly 
diminished their chances in life ? "Mais non," he adds, 
in hi* lively style, "rues beaux Sphex, vous n'avez pas 
ete aussi idiots que cela. Si vous etes de nos jours can- 
tonnes chacun dans un mets de famille, c'est que votre 
ancetre ne vous a pas enseigne la variete." 

He then discusses the alternative whether the 

* " Souv. Entem., troisieme serie." 



250 ORIGIN OF THE HABITS OF SPHEX. 

ancestral Sphex restricted itself to one victim, and 
that its descendants "subdivises en groupes et con- 
stitues enfin en autant d'especes distinctes par le lent 
travail des siecles, se sont avises qu'en dehors du 
comestible des ancetres il y avait une foule d'autres 
aliments." 

This, he says, supposes that they expprimented on 
various victims, found several of them to their liking, 
and then, after a period of varied and plentiful diet, 
voluntarily abandoned so great an advantage. 

"Avoir decouvert, par vos essais d'age en a>e, la 
variete de l'alimentation ; Tavoir pratiquee, au grand 
a vantage de votre race, et finir par l'unifqrmite, cause 
de decadence ; avoir connu l'excellent et le repudier 
pour le mediocre, ' Oh ! mes Sphex, ce serait stupide si 
le transformisme avait raison. ' " 

" J'estime," then he concludes, " que votre ancetre 
commun, votre precurseur, a gouts simples ou bien a 
gouts multiples, est une pure chimere." 

No doubt the habits of Hymenoptera present many 
difficulties, and have undoubtedly many surprises in 
store for us, and I cannot think the matter is so clear 
as M. Fabre imagines, or that he has exhausted the 
possible cases. It is possible, though it is, I admit, 
only a supposition, that the ancestral Sphex hunted 
some species which does not now exist — at lea^t not in 
the south of France — and which might have disappeared 
gradually. As it became rarer, they might be driven 
to attack other prey, and M. Fabre has himself shown 
by a variety of most ingenious experiments that the 
larvae are by no means fastidious as to their food. The 
Hymenoptera vary considerably in size, and the larger 
individuals might be able to overmaster some large 



RACE DIFFERENCES. 251 

insect, while the feebler specimens were compelled to 
content themselves with humbler fare. 

This is no purely imaginary case. M. Fabre himself 
distinguishes three races — or are they species ? — of Leu- 
cospis which live on the three species of Chalicodomas. 

" Venu du Chalicodome des galets ou des rnurailles, 
dont l'opulente larve le sature de nourriture, il merite 
par sa grosseur le nom le Leucospis gigas, que lui 
donne Fabricius ; venu du Chalicodome des hangars, il 
ne merite plus que le nom de Leucospis grandis, que 
lui octroie Klug. Avec une ration moindre, le geant 
baisse d'un degre et n'est plus que le grand. Venu 
du Chalicodome des arbustes, il baisse encore, et si 
quelque nomenclateur s'avisait de le qualifier, il 
n'aurait pins droit qu'au titre de mediocre. 

The Anthrax, again, differs considerably a cording to 
the species on which it has fed, those coming from the 
cocoons of Osmia tricomis being much larger from 
those from 0. cyanea. 

Or it might well happen that while the victim was 
from some cause or other, say for instance the absence 
of food elsewhere, limited to a particular district, the 
region beyond was suited to the ancestress Sphex. In 
that case, would she not naturally try whether she 
could not find some other suitable food ? Tnis again, is 
not a purely imaginary case. M. Fabre himself tells us 
that while " la Scolie interrompue avait pour gibier aux 
environs d'Avignon, la larve de l'Anoxie velue (Anoxia 
villosa). Aux environs de Serignan, dans un sol sablon- 
neux semblable, sans autre vegetation que quelques 
maigres gramens, je lui trouve pour vivres l'Anoxie 
matutinale (Anoxia matutinal is), qui remplace ici la 
velue." 



252 POWER OF DETERMINING SEX. 

That bees soon take to newly introduced flowers is a 
familiar case which every one must have noticed, and 
which it is surely not logical to dismiss by the conve- 
nient process of referring it to " instinct." It is indeed 
difficult for any one who watches these insects to deny 
to bees the possession of a higher and conscious faculty. 

In considering the question whether these remarkable 
instincts were originally, so to say, engrafted in the 
insect, or whether they were the result of innumerable 
repetitions of similar actions carried on by a long 
series of ancestors, we may perhaps be aided by the 
consideration that, though the results would in either 
case be in many respects the same, there are some in 
which they would altogether differ. In the former, for 
instance, we might expect that the insect would be so 
gifted that no slight obstacle should interfere with the 
great end in view : in the latter, on the contrary, the 
very repetition which gave such remarkable results 
would tend to incapacitate the insect from dealing with 
any unusual conditions. 

Limitation of Instinct. 

We should, in fact, find side by side with these won- 
derful instincts almost equally surprising evidence of 
stupidity. Now, one species of Sphex preys on a large 
grasshopper (Ephippigera). Having disabled her vic- 
tim, she drags it along by one of the antennae, and 
M. Fabre found that if the antennae be cut off close to 
the head, the Sphex, after trying in vain to get a grip, 
gives the matter up as a bad job, and leaves her victim 
in despair, without ever think'ng of dragging it by one 
of its legs. Again, when a Sphex had provisioned her 
cell, laid her egg, and was about to close it up, M, 



LIMITATION OF INSTINCT. 253 

Fabre drove her away, and took out both the Ephippi- 
gera and the egg. He then allowed the Sphex to return. 
She went down into the empty cell, and though she 
must have known that the grasshopper and the egg 
were no longer there, yet she proceeded calmly to stop 
up the orifice just as if nothing had happened. 

The genus Sphex paralyzes its victims and provisions 
its cell once for all. Bembex, on the contrary, as 
already mentioned, kills the insects on which its young- 
are to feed, and, perhaps on this account, brings its 
young fresh food (mainly flies) from time to time. 
But while the Bembex thus preys on some flies, there 
are others which avenge their order. The genus 
Miltogramma lays its eggs in the cell of the Bembex; 
and, though there seems no reason why the Bembex, 
which is by far the stronger insect, should tolerate this 
intrusion, which, moreover, she shows unmistakably to 
be most unpalatable, she never makes any attack on 
her enemy. Nay, when the young of the Miltogramma 
are hatched, so far from being killed or removed, these 
entomological cuckoos are actually fed until they reach 
maturity. Nevertheless, it seems contrary to etiquette 
for the fly to enter the cell of the Bembex ; she watches 
the opportunity when the latter is in the cell and is 
dragging down the victim. Then is the Miltogramma's 
opportunity; she pounces on the victim, and almost 
instantaneously lays on it two or three eggs, which are 
then transferred, with the insect on which they are to 
feed, to the cell. 

It is remarkable how the Bembex remembers (if one 
may use such a word) the entrance to her cell, covered 
as it is with sand, exactly to our eyes like that all 
ronnd. On the other hand, M . Fabre found that if he 



254 TOLERATION OF PARASITES. 

removed the surface of the earth and the passage, 
exposing the cell and the larva, the Bembex was quite 
at a loss, and did not even recognize her own offspring. 
It seems as if she knew the door, the nursery, and the 
passage, but not her child. 

Another ingenious experiment of M. Fabre's was 
made with a mason bee (Chalicodoma). This genus 
constructs an earthen cell, through which at maturity 
the young insect eats its way. M. Fabre found that if 
he pasted a piece of paper round the cell, the insect had 
no difficulty in eating through it ; but if he enclosed the 
cell in a paper case, so that there was a space even of 
only a few lines between the cell and the paper, in that 
case the paper formed an effectual prison. The instinct 
of the insect taught it to bite through one enclosure,, 
but it had not wit enough to do so a second time. 

One of the most striking instances of stupidity 
(may I say) is mentioned by M. Fabre, in the case of 
one of bis favourite bees, the Chalicodoma pyrenaica. 
This species builds cells of masonry, which she tills with 
honey as she goes on, raising the rim a little, then 
making a few journeys for honey, then raising the rim 
again, and so on until the cell is completed. She then 
prepares a last load of mortar, brings it in her mandibles, 
lays her egg,- and immediately closes up the cell; 
having doubtless provided the mortar beforehand, lest 
during her absence an enemy should destroy the egg 
or any parasitic insect should gain admittance. This 
being so, M. Fabre chose a cell which was all but 
finished, and during the absence of the bee he broke 
away part of the cell-covering. Again, in some half- 
finished cells he broke away a little of the wall. In 
all these cases the bee, as might be expected, repaired 



CASES OF APPARENT STUPIDITY. 255 

the mischief, the operation being in the natural order 
of her work. But now conies the curious fact. In 
another series of cells M. Fabre pierced a hole in the cell 
below the part where the bee was working, and through 
which the honey at once began to exude. The poor 
stupid little bee, however, never thought of repairing 
the breach. She worked on as if nothing had happened. 
In her alternate journeys she brought first mortar and 
then honey, which, however, ran out again as fast as it 
was poured in. This experiment he repeated over and 
over again with various modifications in detail, but 
always with the same result. It may be suggested that 
possibly the bee was unable to stop up a hole once 
formed. But that could not have been the case. M. 
Fabre took one of the pellets of mortar brought by the 
bee, and successfully stopped the hole himself. The 
omission, therefore, w y as due, not to a want of power, 
but of intellect. But M. Fabre carried his experiment 
still further. Perhaps the bee had not noticed the injury. 
He chose, therefore, a cell which was only just begun 
and contained very little honey. In this he made a 
comparatively large hole. The bee returned with a 
supply of honey, and, seeming much surprised to find 
the hole in the bottom of the cell, examined it carefully, 
felt it with her antennae, and even pushed them through 
it. Did she then, as might naturally have been expected, 
stop it up ? Not a bit. The unexpected catastrophe 
transcended the range of her intellect, and she calmly 
proceeded to pour into this vessel of the Danaides load 
after load of honey, which of course ran out of the bottom 
as fast as she poured it in at the top. All the afternoon 
she laboured at this fruitless task, and began again 
undiscouraged the next morning. At length, when she 
13 



256 M. FABRE'S EXPERIMENTS. 

had brought the usual complement of honey, she laid 
her egg, and gravely sealed up the empty cell. In 
another case, he made a large hole in the cell just above 
the level of the honey — a hole so large that through it 
he was able to see the bee lay her egg. Having done so, 
she carefully closed the top of the cell, but though she 
closely examined the hole in the side, it did not enter 
into the range of her ideas that such an accident could 
take place, and it never occurred to her to cover it up. 

Another curious point raised by these ingenious 
experiments has reference to the quantity of honey. 
The cell is by no means filled ; a space is always left 
between the honey and the roof of the cell. The usual 
depth of the honey in a completed cell is ten milli- 
metres. But the bee is not guided by this measure- 
ment, for in the preceding cases she sometimes closed 
the cell when the honey had a depth of only five milli- 
metres, of three, or even when the cell was almost empty. 
No ; in some mysterious manner the bee feels when she 
has provided as much honey as her ancestress had done 
before her, and regards her work as accomplished. 
What a wonderful, but what a narrow, nature ! She 
has built the cell and provided the honey, but there 
her instinct stops: if the cell is pierced, if the h< ney is 
removed, it does not occur to her to repair the one or 
fill up the other. M. Fabre not unnaturally asks, 
" Avec la moindre lueur rationnelle, Finsecte deposerait- 
il son oeuf sur le tiers, sur le dixieme des vivres neces- 
saires ; le deposerait-il dans une cellule vide ; laisserait- 
il le nourrisson sans nourriture, incroyable aberration de 
la maternite ? J'ai raconte, que le lecteur decide/ 5 

The family of bees is generally reckoned to be one 
of great intelligence, but these and many other similar 



LIMITATION OF INSTINCT. 257 

instances which might be recorded seem to show great 
limitation of intelligence. 

Let me give one other, which any person may easily 
test for himself. I took a glass shade or jar eighteen 
inches long, and with a mouth six and a half inches 
wide, turning the closed end to the window, and put in 
a common hive bee. She buzzed about for an hour, 
when, as there seemed no chance of her getting out, 
I put her back into the hive. Two flies, on the 
contrary, which I put in with her, got out at once. 
Again I put another bee and a fly into the same glass ; 
the latter flew out at once. For half an hour the 
bee tried to get out at the closed end ; I then turned 
the glass wdth its open end to the light when she flew 
out at once. To make sure, I repeated the experiment 
once more, with the same result. 

And yet there is, no doubt, ample foundation for the 
ordinary view which attributes considerable intelligence 
to the bee, within the sphere of her own operations. 

Several other points of resemblance between 
instincts and habits could be pointed out. As in 
repeating a well-known song, so in instincts, one action 
follows another by a sort of rhythm. If a person be 
interrupted in a song, or in repeating anything by rote, 
he is often forced to go back to recover the habitual 
train of thought; so P. Huber found it was with a 
caterpillar, which makes a very complicated hammock; 
for if he took a caterpillar which had completed its 
hammock up to, say, the sixth stage of construction, 
and put it into a hammock completed up only to the 
third stage, the caterpillar simply re-performed the 
fourth, fifth, and sixth stages of construction. "If, how- 
ever, a caterpillar were taken out of a hammock made 



258 INSTINCTS AND HABITS. 

up, for instance, to the third stage, and were put into 
one finished up to the sixth stage, so that much of its 
work was already done for it, far from feeling the 
benefit of this, it was much embarrassed, and, in order 
to complete its hammock, seemed forced to start from 
the third stage, where it had left off, and thus tried to 
complete the already finished work."* 

Another very interesting series of observations which 
we owe to M. Fabre has reference to the question of 
sex, and it would really seem that the mother can 
regulate the sex of the egg at will. In many of our 
wild bees, the females are much larger than the males. 
The male lives a life of pleasure, idle but short. 
" Quinze jours de bombance dans un magasin a miel, 
un an de sommeil sous terre, une minute d'amour au 
soleil, puis la mort." 

But the female " C'est la mere, la mere seule qui, 
peniblement, creuse sous terre des galeries et des 
cellules, petrit le stuc pour enduire les loges, ma£onne 
la demeure de ciment et de graviers, taraude le bois et 
subdivise le canal en etages, de 'oupe des rondelles de 
feuilles qui seront assemblies en pots a miel, malaxe 
la resine cueillie en larmes sur les blessures des pins 
pour edifier des voutes dans la rarope vide d'un es- 
cargot, chasse la proie, la paralyse et la traine au 
logis, cueille la poussiere pollinique, elabore le miel 
dans son jabot, emmagasine et mixtionne la patee. 
Ce rude labeur, si imperieux, si actif, dans lequel se 
depense toute la vie de l'insecte, exige, c'est evident, 
une puissance corporelle bien inutile au male, l'amou- 
ieux desoeuvre." 

In the hive bee the drone cells differ materially in 
shape from those of the queens and workers. 

* Darwin, " Origin of Species." 



INFLEXIBILITY OF INSTINCT. 259 

In the solitary wasps, where the females are much 
larger than the males, the mother builds a larger cell and 
provides more food for the former than for the latter. 

The Chalicodoma (one of the mason bees) often lays 
her eggs in old cells of the previous year. These 
are of two sizes — large ones, originally built for the 
females, and small ones for the males. Now, in 
utilizing old cells, the bee always places male eggs in 
male cells and female eggs in female cells. If, how- 
ever, a female cell be cut down so as to reduce the 
size, then indeed the bee deposits in it a male egg. 

The bees belonging to the genus Osmia* arrange 
their cells in a row in a hollow stick, or some other 
similar situation, and it has long been known that in 
these and similar cases the cells first provisioned, and 
which are therefore furthest from the entrance, always 
contain females, while the outer cells always contain 
males. 

There is an obvious advantage in this, because the 
males come out a fortnight or more before the females, 
and it is, of course, convenient that those which have 
to come out first should be in the cells nearest the 
door. The bee does not, however, lay all the female 
eggs first, and then all the male eggs. By no means. 
She produces altogether from fifteen to thirty eggs, but 
seldom arranges them in one row; generally they are 
in several series, and in every one the same sequence 
occurs — females further from, and males nearest to, the 
door. 

For instance, one of M. Fabre's marked bees — one, 
moreover, of exceptional fertility — occupied some glass 

* Osmia tridentata constitutes an exception to the general rule in 
this respect, as in some others. 



260 DIFFERENT HABITS OF MALES AND FEMALES. 

tubes, which he arranged conveniently for her. From 
the 1st to the 10th of May she constructed, in one tube, 
eight cells — first seven female, and then one male. 
From the 10th to the 17th, in a second tube, she built 
first three female and then three male cells; from the 
17th to the 25th, in a third, three female and then 
two male ; on the 26th, in a fourth, one female ; and, 
finally, from the 26th to the 30th, in a fifth, two female 
and three male : altogether twenty-five, seventeen 
female and eight male cells. 

The advantage of this is clear, but the manner in 
which it is secured is not so obvious. It might be 
suggested that the quantity of food was not regulated 
by the sex of the young one, but that the sex depended 
on the quantity of food. This would be very improb- 
able, and M. Fabre attempted to disprove it by some 
very ingenious experiments. He found that if he took 
some of the food from a female cell, the bee or wasp 
produced was still a female, though a starveling; while 
if he added food to a male cell, the larva still pro- 
duced a male, though a very large and fine one. 

M. Fabre then made some of his most ingenious 
experiments. He brought into his room a large number 
of cocoons of Osmia. When the perfect insects were 
about to emerge, he arranged for them a number of 
glass tubes, of which the Osmias gladly availed them- 
selves, and in which they proceeded to construct their 
cells. The usual arrangement, as already mentioned, 
is that the males are placed nearest to, and the female 
furthest from, the door. But M. Fabre so arranged 
the tubes that each was in two parts, an outer wider 
portion having a diameter of eight to twelve milli- 
metres, which is sufficient for a female cell ; and an 



ARRANGEMENT OF MALE AND FEMALE CELLS. 261 

inner narrower portion with a diameter of five to five 
and a half millimetres, which is too small for a female, 
but just large enough for a male. This arrangement 
placed the Osmias in a difficulty. They could not 
follow their natural instinct and construct at the end 
of the tube cells large enough for females. 

What happened ? Some of the Osmias shut off the 
narrow ends, and used only the outer wider portion. 
Others, reluctant, as it were, to throw away a chance, 
built also in the narrow part of the tube, and under 
these circumstances, contrary to the otherwise invari- 
able rule, the inner and first constructed cells contained 
males. 

M. Fabre concludes then, and it 'seems to me has 
given very strong reasons for thinking so, that these 
privileged insects not only know the sex of the insect 
which will emerge from the egg they are about to lay, 
but that at their own will they can actually control it ! 
Certainly a most curious and interesting result ! 

He concludes his charming work as follows :— " Mes 
chers insectes, dont l'etude m ? a soutenu et continue a 
me soutenir au milieu de mes plus rudes epreuves, il 
faut ici, pour aujourd'hui, se dire adieu. Autour de 
moi les rangs s'eclaircissent et les longs espoirs ont fui. 
Pourrai-je encore parler de vous ? " and every lover of 
nature will, I am sure, echo the wish. 



CHAPTER XIIL 

ON THE SUPPOSED SENSE OF DIRECTION. 

One of the most interesting questions connected with 
the instincts and powers of animals has reference to the 
manner in which they find their way back, after having 
been carried to a distance from, home. This has by 
some been attributed to the possession of a special 
" sense of direction." 

Mr. Darwin suggested that it would be interesting 
to try the effect of putting animals u in a circular box 
with an axle, which could be made to revolve very 
rapidly, first in one direction and then in another, so 
as to destroy for a time all sense of direction in the 
insects. I have sometimes," he said, "imagined that 
animals may feel in which direction they were at the 
first start carried. M In fact, in parts of France it is 
considered that if a cat is carried from one house to 
another in a bag, and the bag is whirled round and 
round, the cat loses her direction and cannot return to 
her old home. 

On this subject M. Fabre has made some interesting 
and amusing experiments. He took ten bees belonging 
to the genus Ohalicodoma, marked them on the back 
with a spot of white, and put them in a bag. He 
then carried them half a kilometre in one direction, 
stopping at a point where an old cross stands by the 



EXPEKIMENTS WITH BEES. 263 

wayside, and whirled the bag rapidly round his head. 
While he was doing so a good woman came by, who 
was not a little surprised to find the professor stand- 
ing in front of the old cross, solemnly whirling a bag- 
round his head, and, M. Fabre fears, strongly suspected 
him of some satanic practice. However this may be, 
M. Fabre, having sufficiently whirled his bees, started off 
back in the opposite direction, and carried his prisoners 
to a distance from their home of three kilometres. 
Here he again whirled them round, and then let them 
go one by one. They made one or two turns round 
him, and then flew off in the direction of home. In the 
meanwhile his daughter Antonia was on the watch. 
The first bee did the mile and three-quarters in a 
quarter of an hour. Some hours after two more re- 
turned ; the other seven did not reappear. 

The next day he repeated this experiment with ten 
other bees. The first returned in five minutes, and two 
more in about an hour. In this case, again, seven out 
of ten failed to find their way home. 

In another experiment he took forty-nine bees. 
When let out, a few started wrong, but he says that 
"lorsque la rapidite du vol me laisse reconnaitre la 
direction suivie ; " the great majority flew homewards. 
The first arrived in fifteen minutes. In an hour and 
a half eleven had returned, in five hours six more, 
making seventeen out of forty-nine. Again he experi- 
mented with twenty, of which seven found their way 
home. In the next experiment he took the bees rather 
further — to a distance of about two and a quarter miles. 
In an hour and a half two had returned, in three hours 
and a half seven more ; total, nine out of forty. Lastly, 
he took thirty bees: fifteen marked rose he took by 



264 WHIRLING BEES. 

a roundabout route of over five miles ; the other fifteen 
marked blue he sent straight to the rendezvous, about 
one and a half miles from home. All the thirty were 
let out at noon ; by five in the evening seven " rose " 
bees and six " blue " bees had returned, so that the 
long detour had made no appreciable difference. 
These experiments seem to M. Fabre conclusive. " La 
demonstration," he says, " est suffisante. Ni les mouve- 
ments enchevetres d'une rotation comme je l'ai decrite ; ni 
l'obstacle de collines a franchir et de bois a traverser; ni 
les embuches d'une voie qui s'avance, retrograde et revient 
par un ample circuit, ne peuvent troubler les Chali- 
codomes depayses et les empecher de revenir.au nid."* 
I am not ashamed to confess that, charmed by M. 
Fabre's enthusiasm, dazzled by his eloquence and 
ingenuity, I was at first disposed to adopt this view. 
Calmer consideration, however, led me to doubt, and 
though M. Fabre's observations are most ingenious, 
and are very amusingly described, they do not carry 
conviction to my mind. There are two points specially 
to be considered — 

1. The direction taken by the bees when released. 

2. The success of the bees in making good their 
return home. 

As regards the first point, it will be observed that the 
successful bees were in the following proportion, viz. : — 



3 out of 10 


4 


„ 10 


17 


, 49 


7 


, 20 


9 


, 40 


7 


, 15 


Or altogether 47 


„ 144 



J. H. Fabre, " Nouveaux Souvenirs Entomologiques." 



BEHAVIOUR OF BEES IF TAKEN FROM HOME. 265 

This is not a very large proportion. Out of the 
whole number no less than ninety-seven appear to 
have lost their way. May not the forty-seven have 
found theirs by sight or by accident ? Instinct, how- 
ever inferior to reason, has the advantage of being 
generally unerring. When two out of three bees went 
wrong, we may, I think, safely dismiss the idea of 
instinct. Moreover, the distance from home was only 
one and a half to two miles. Now, bees certainly 
know the country for some distance round their home ; 
how far they generally forage I believe we have no 
certain information, but it seems not unreasonable to 
suppose that if they once came within a mile of their 
nest they would find themselves within ken of some 
familiar landmark. Now, if we suppose that 150 bees 
are let out two miles from home, and that they flew 
away at random, distributing themselves equally in all 
directions, a little consideration will show that some 
twenty-five of them would find themselves within a mile 
of home, and consequently would know where they were. 
I have never myself experimented with Chalicodomas, 
but I have observed that if a hive bee is taken to a 
distance, she behaves as a pigeon does under similar 
circumstances ; that is to say, she flies round and round, 
gradually rising higher and higher and enlarging her 
circle, until I suppose her strength fails or she comes 
within sight of some known object. Again, if the bees 
had returned by a sense of direction, they would have 
been back in a few minutes. To fly one and a half or 
two miles would not take five minutes. One bee out of 
the 147 did it in that time ; but the others took one, 
two, three, or even five hours, Surely, then, it is 
reasonable to suppose that these lost some time before 



266 MODE OF FINDING THEIR WAY. 

they came in sight of any object known to them. The 
second result of M. Fabre's observations is not open to 
these remarks. He observes that the great majority 
of his Chalicodomas at once took the direction home. 
He confesses, however, in the sentence I have already 
quoted, that it is not always easy to follow bees with 
the eye. Admitting the fact, however, it seems to me 
far from impossible that the bees knew where they 
were ; and, at any rate, this does not seem so improbable 
that we should be driven to admit the existence of a 
new sense 5 which we ought only to assume as a last 
resource. 

Moreover, M. Fabre himself says, " Lorsque la rapidite 
du vol me laisse reconnaitre la direction suivie," which 
seems to imply a doubt. Indeed, some years previously 
he had made a similar experiment with the same 
species, but taking them direct to a point rather over 
two miles (four kilometres) from the nest, and not 
whirling them round his head. I looked back, there, 
fore, to his previous work to see how these behaved, 
and I found that he says — 

"Aussitot libres, les Chalicodomes fuient, comme 
effares, qui dans une direction, qui dans la direction 
tout opposee. Autant que le permet leur vol fougueux, 
je crois neanmoins reconnaitre un prompt retour des 
abeilles lancees a l'oppose de leur demeure, et la majorite 
me semble se diriger du cote de l'horizon ou se trouve 
le nid. Je laisse ce point awe des doutes, que rendent 
inevitables des insectes perdus de vue a une vingtaine 
de metres de distance." 

In this case, then, some went in one direction, some 
in another. It certainly would be remarkable if bees 
which were taken direct missed their way, while those 



EXPERIMENTS WITH ANTS. 267 

which were whirled round and round went straight 
home. 

Moreover, it appears that after all, as a matter of fact, 
they did not fly straight home. If they had done so they 
would have been back in three or four minutes, whereas 
they took far longer. Even then, if they started in the 
right direction, it is clear that they did not adhere 
to it. I have myself tried experiments of the same 
kind with hive bees and ants. For instance, I put 
down some honey on a piece of glass close to a nest 
of Lasius niger, and when the ants were feeding I 
placed it quietly on the middle of a board one foot 
square, and eighteen inches from the nest. I did 
this with thirteen ants, and marked the points at 
which they left the board. Five of them did so on 
the half of the board nearest the nest, and eight on 
that turned away from it. I then timed three of 
them. They all found the nest eventually, but it took 
them ten, twelve, and twenty minutes respectively. 
Again, I took forty ants which were feeding on some 
honey, and put them down on a gravel-path about fifty 
yards from the nest, and in the middle of a square 
eighteen inches in diameter, which I marked out on 
the path by straws. 

I prepared a corresponding square on paper, and, 
having indicated by the arrow the direction of the nest, 
I marked down the spot where each ant passed the 
boundary. They crossed it in all directions; and 
dividing the square into two halves, one towards the 
nest and one away from it, the number in each were 
almost exactly the same. 

After leaving the square, they wandered about with 
every appearance of having lost themselves, and crossed 



268 ME. ROMANES 5 EXPERIMENTS. 

the boundary backwards and forwards in all directions. 
Two of them, however, we watched for an hour each. 
They meandered about, and at the end of the time 
one was about two feet from where she started, but 
scarcely any nearer home; the other about six feet 
away, and nearly as much further from home. I then 
took them up and replaced them near the nest, which 
they at once joyfully entered. 

I mentioned some of the foregoing facts in a paper 
which I read at the meeting of the British Association 
at Aberdeen, and they have since been confirmed by 
Mr. Bomanes.* 

" In connection," he says, " with Sir John Lubbock's 
paper at the British Association, in which this subject 
is treated, it is perhaps worth while to describe some 
experiments which I made last year. The question to 
be answered is whether bees find their way home 
merely by their knowledge of landmarks, or by means 
of some mysterious faculty usually termed a sense of 
direction. The ordinary impression appears to have 
been that they do so in virtue of some such sense, and 
are therefore independent of any special knowledge of 
the district in which they may be suddenly liberated ; 
and, as Sir John Lubbock observes, this impression was 
corroborated by the experiments of M. Fabre. The 
conclusions drawn from these experiments, however, 
appeared to me, as they appeared to Sir John, un- 
warranted by the facts ; and therefore, like him, I re- 
peated them with certain variations. In the result I 
satisfied myself that the bees depend entirely upon their 
special knowledge of district or landmarks, and it is 
because my experiments thus fully corroborate those 

* Nature, October 29, 1886. 



MR. ROMANES' EXPERIMENTS. 269 

which were made by Sir John that it now occurs to me 
to publish them. 

"The house where I conducted the observations is 
situated several hundred yards from the coast, with 
flower-gardens on each side, and lawns between the 
house and the sea. Therefore bees starting from the 
house would find their honey on either side of it, while 
the lawns in front would be rarely or never visited — 
being themselves barren of honey, and leading only to 
the sea. Such being the geographical conditions, I 
placed a hive of bees in one of the front rooms on the 
basement of the house. When the bees became 
thoroughly well acquainted with their new quarters by 
flying in and out of the open window for a fortnight, I 
began the experiments. The modus operandi consisted 
in closing the window after dark when all the bees were 
in their hive, and also slipping a glass shutter in front 
of the hive door, so that all the bees were doubly im- 
prisoned. Next morning I slightly raised the glass 
shutter, thus enabling any desired number of bees to 
escape. When the desired number had escaped, the 
glass shutter was again closed, and all the liberated 
bees were caught as they buzzed about the inside of the 
shut window. These bees were then counted into a box, 
the window of the room opened, and a card well smeared 
over with birdlime placed upon the threshold of the 
beehive, or just in front of the closed glass shutter. 
The object of all these arrangements was to obviate the 
necessity of marking the bees, and so to enable me not 
merely to experiment with ease upon any number of 
individuals that I might desire, but also to feel confident 
that no one individual could return to the hive un- 
noticed. For whenever a bee returned it was certain 



270 MR. ROMANES' EXPERIMENTS. 

to become entangled in the bird-lime, and whenever I 
found a bee so entangled, I was certain that it was one 
which I had taken from the hive, as there were no other 
hives in the neighbourhood. 

" Such being the method, I began by taking a score oi 
bees in the box out to sea, where there could be no land- 
marks to guide the insects home. Had any of these 
insects returned, I should next have taken another score 
out to sea (after an interval of several days, so as to be 
sure that the first lot had become permanently lost), 
and then, before liberating them, have rotated the box 
in a sling for a considerable time, in order to see whether 
this would have confused their sense of direction. But, 
as none of the bees returned after the first experiment, 
it was clearly needless to proceed to the second. Ac- 
cordingly, I liberated the next lot of bees on the sea- 
shore, and, as none of these returned, I liberated another 
lot on the lawn between the shore and the house. I 
was somewhat surprised to find that neither did any of 
these return, although the distance from the lawn to 
the hive was not above two hundred yards. Lastly, I 
liberated bees in different parts of the flower-garden, 
and these I always found stuck upon the bird-lime 
within a few minutes of their liberation. Indeed, they 
often arrived before I had had time to run from the 
place where I had liberated them to the hive. Now, 
as the garden was a large one, many of these bees had 
to fly a greater distance, in order to reach the hive, 
than was the case with their lost sisters upon the lawn, 
and therefore I could have no doubt that their uniform 
success in finding their way home so immediately was 
due to their special knowledge of the flower-garden, 
and not to any general sense of direction. 



NO EVIDENCE OF SEPARATE SENSE OF DIRECTION. 271 

"Imay add that, while in Germany a few weeks ago, 
I tried on several species of ant the same experiments 
as Sir John Lubbock describes in his paper as having 
been tried by him upon English species, and here also I 
obtained identical results; in all cases the ants were 
hopelessly lost if liberated more than a moderate dis- 
tance from their nest. 

M. Eomanes' experiments, therefore, as he himself 
says, entirely confirm the opinion I have ventured to 
express — that there is no sufficient evidence among 
insects of anything which can justly be called a " sense 
of direction." 



CHAPTER XIV. 

ON THE INTELLIGENCE OF THE DOG. 

Consideking the long ages during which roan and 
the other animals have shared this beautiful world, 
it is surely remarkable how little we know about them. 
We have recently had various interesting works on 
the intelligence and senses of animals, and yet I think 
the principal impression which they leave on the mind 
is that we know very little indeed on the subject. 

The Dog. 

As to the intelligence of the dog, a great many 
people, indeed, seem to me to entertain two entirely 
opposite and contradictory opinions. I often hear it 
said that the dog, for instance, is very wise and clever. 
But when I ask whether a dog can realize that two and 
two make four, which is a very simple arithmetical 
calculation, I generally find much doubt expressed. 

That the dog is a loyal, true, and affectionate friend 
must be gratefully admitted, but when we come to con- 
sider the psychical nature of the animal, the limits of our 
knowledge are almost immediately reached. I have else- 
where suggested that this arises in great measure from 
the fact that hitherto we have tried to teach animals, 
rather than to learn from them — to convey our ideas to 



EDUCATION OF THE DEAF AND DUMB. 273 

them, rather than to devise any language or code of 
signals by means of which they might communicate 
theirs to us. The former may be more important 
from a utilitarian point of view, though even this is 
questionable, but psychologically it is far less interest- 
ing. Under these circumstances, it occurred to me 
whether some such system as that followed with deaf 
mutes, and especially by Dr. Howe with Laura Bridg- 
man, might not prove very instructive if adapted to the 
case of dogs. 

A very interesting account of Laura Bridgman has 
been published by Wright, compiled almost entirely from 
reports of the Perkins Institution, and the Massachusetts 
Asylum for the Blind, in which Dr. Howe, the director 
of the establishment, details the history of Laura Bridg- 
man, who was deaf, dumb, and blind, almost without the 
power of smell and taste, but who, nearly alone among 
those thus grievously afflicted, possessed an average, if 
not more than an average, amount of intelligence, 
although, until brought under Dr. Howe's skilful treat- 
ment and care, her physical defects excluded her from 
all social intercourse. 

Laura Bridgman was born of intelligent and respect- 
able parents, in Hanover, New Hampshire, U.S., in 
December, 1829. She is said to have been a sprightly, 
pretty infant, but subject to fits, and altogether very 
fragile. At two years old she was fairly forward, had 
mastered the difference between A and B, and, indeed, 
is said to have displayed a considerable degree of 
intelligence. She then became suddenly ill, and had 
to be kept in a darkened room for five months. When 
she recovered she was blind, deaf, and had nearly lost 
the power both of smell and taste. 



274 LAUKA BKIDGMAN. 

"What a situation was hers! The darkness and 
silence of the tomb were around her ; no mother's smile 
gladdened her heart, or ' called forth an answering 
smile;' no father's voice taught her to imitate his 
sounds. To her, brothers and sisters were but forms 
of matter, which resisted her touch, but which differed 
not from the furniture of the house, save in warmth 
and in the power of locomotion, and in these respects 
not even from the dog or cat." 

Her mind, however, was unaffected, and the sense 
of touch remained. " As soon as she was able to walk, 
Laura began to explore the room, and then the house ; 
she became familiar with the form, density, weight, 
and heat of every article she could lay her hands on. 

"She followed her mother, felt her hands and arms, 
as she was occupied about the house, and her disposi- 
tion to imitate led her to repeat everything herself. 
She even learnt to sew a little, and to knit. Her 
affections, too, began to expand, and seemed to be 
lavished upon the members of her family with peculiar 
force. 

" The means of communication with her, however, 
were very limited. She could only be told to go to 
a place by being pushed, or to come to one by a sign 
of drawing her. Patting her gently on the head 
signified approbation ; on the back, the contrary." 

The power of communication was thus most limited, 
and her character began to suffer, when fortunately Dr. 
Howe heard of her, and in October, 1837, received her 
into the institution. 

"For a while she was much bewildered, till she became 
acquainted with her new locality, and somewhat familiar 
with the inmates ; the attempt was made to give h^r 



LAURA BRIDGMAN. 275 

knowledge of arbitrary signs, by which she could 
interchange thoughts with others. 

"The first experiments were made by taking the 
articles in common use, such as knives, forks, spoons, 
keys, etc., and pasting upon them labels, with their 
names embossed in raised letters. These she felt 
carefully, and soon, of course, distinguished that the 
crooked lines s-p-o-o-n differed as much from the 
crooked lines k-e-y, as the spoon differed from the key 
in form. Then small detached labels with the same 
words printed upon them were put into her hands; 
she soon observed tbat they w 7 ere the same as those 
pasted upon the articles. She showed her perception 
of this similarity by laying the label k-e-y upon the 
key, and the label s-p-o-o-n upon the spoon. 

"Hitherto, the process had been mechanical, and the 
success about as great as that of teaching a very know- 
ing dog a variety of tricks. 

"The poor child sat in mute amazement, and patiently 
imitated everything her teacher did. But now her 
intellect began to work, the truth flashed upon her, and 
she perceived that there was a way by which she could 
herself make a sign of anything that was in her own 
mind, and show it to another mind. At once her 
countenance lighted up with a human expression. It 
was no longer as a mere instinctive animal ; it was an 
immortal spirit, eagerly seizing upon a new link of 
union with other spirits. I conld almost fix upon the 
moment when this truth dawned upon her mind, and 
spread its beams upon her countenance ; I saw that the 
great obstacle was overcome, and that henceforth 
nothing but patient and persevering, but plain and 
straightforward, efforts were necessary. 



276 APPLICATION OF THE METHOD FOLLOWED 

"The result, thus far, is quickly related and easily 
conceived ; but not so was the process, for many weeks 
of apparently unprofitable labour were spent before it 
was effected. 

" The next step was to procure a set of metal types, 
with the different letters of the alphabet cast separately 
on their ends ; also a board, in which were square holes, 
into which she could set the types, so that the letters 
could alone be felt above the surface. 

" Thus, on any article being handed to her, as a pencil 
or watch, she would select the component letters and 
arrange them on the board, and read them with apparent 
pleasure, assuring her teacher that she understood by 
taking all the letters of the word and putting them to 
her ear, or on the pencil." 

It is unnecessary, from my present point of view, to 
carry the narrative further, interesting as it is. I will 
only observe that even in the case of Laura Bridgman 
the process was one of much difficulty and requiring 
great patience. For a long while it was found im- 
possible to make her realize the use of adjectives; she 
could not "understand any general expression of 
quality." Again, we are told that " Some idea of the 
difficulty of teaching her common expressions may be 
derived from the fact that a lesson of two hours upon 
the words ' right' and 'left' was deemed very profitable 
if she had in that time really mastered the idea." 

Now, it seemed to me that the ingenious method 
devised by Dr. Howe, and so successfully carried 
out in the case of Laura Bridgman, might be adapted 
to the case of dogs, and I have tried this in a small 
way with a black poodle named Van. 



WITH THE DEAF AND DUMB TO ANIMALS. 277 

Van and his Cards. 

I took two pieces of cardboard about ten inches by 
three, and on one of them printed in large letters the 
word 



FOOD 



leaving the other blank. I then placed the two 
cards over two saucers, and in the one under the 
"food" card put a little bread and milk, which 
Van, after having his attention called to the card, 
was allowed to eat. This was repeated over and over 
again till he had had enough. In about ten days he 
began to distinguish between the two cards. I then 
put them on the floor and made him bring them to 
me, which he did readily enough. When he brought 
the plain card I simply threw it back, while when he 
brought the " food " card I gave him a piece of bread, 
and in about a month he had pretty well learned to 
realize the difference. I then had some other cards 
printed with the words "out," "tea," "bone," " water," 
and a certain number also with words to which 
1 did not intend him to attach any significance, such 
as "nought," "plain," "ball," etc. Van soon learned 
that bringing a card was a request, and soon learned 
to distinguish between the plain and printed cards ; 
it took him longer to realize the difference between 
words, but he gradually got to recognize several, such 
as " food," " out," " bone," " tea," etc. If he was asked 
whether he would like to go out for a walk, he would 
joyfully fish up the "out" card, choosing it from 
several others, and bring it to me, or run with it in 
evident triumph to the door. 



278 MY DOG VAN. 

I need hardly say that the cards were not always put 
m the same places. They were varied quite indiscrimi- 
nately and in a great variety of positions. Nor could 
the dog recognize them by scent. They were all alike, 
and all continually handled by us. Still, I did not trust 
to that alone, but had a number printed for each word. 
When, for instance, he brought a card with " food " on 
it, we did not put down the same identical card, but 
another bearing the same word ; when he had brought 
that, a third, then a fourth, and so on. For a single 
meal, therefore, eighteen or twenty cards would be 
used, so that he evidently is not guided by scent. No 
one who has seen him look down a row of cards and 
pick up the one he wanted could, I think, doubt that 
iu bringing a card he felt that he is making a 
request, and that he could not only distinguish one 
card from another but also associate the word and 
object. 

I used to leave a card marked " water" in my dress- 
ing-room, the door of which we used to pass in going 
to or from my sitting-room. Van was my constant 
companion, and passed the do r when I was at home 
several times in the day. Generally he took no heed 
of the card. Hundreds, or I may say thousands, of 
times he passed it unnoticed. Sometimes, however, he 
would run in, pick it up, and bring it to me, when of 
course I gave him some water, and on such occasions I 
invariably found that he wanted to drink. 

I might also mention, in corroboration, that one 
morning he seemed unwell. A friend, being at break- 
fast with us, was anxious to see him bring his cards, and 
I therefore pressed him to do so. To my surprise he 
brought three dummy cards successively, one marked 



COMMUNICATION BY MEANS OF CARDS. 279 



"ham," one "bag," and one "brush." I said re- 
proachfully, " Ob, Van ! bring " food," or " tea ; " on 
which he looked at me, went very slowly, and brought 
the "tea" card. Bat when I put some tea down as 
usual, he would not touch it. Generally he greatly 
enjoyed a cup of tea, and, indeed, this was the only 
time I ever knew him refuse it. 

A definite numerical statement always seems to me 
clearer and more satisfactory than a mere general 
assertion. I will, therefore, give the actual particulars 
of certain days. Twelve cards were put on the floor, 
one marked "food" and one "tea." The others had more 
or less similar words. I may again add that every time 
a card was brought, another similarly marked was put 
in its place. Van was not pressed to bring cards, but 
simply left to do as he pleased. 

'Tea" 2 times. 



1 


Van 


brought 


" food 


' 4 times. 


2 




»» 


»> 


6 


»> 


3 




» 


» 


8 


» 


4 




y* 


» 


7 


»> 


5 




>» 


J5 


6 


» 


6 




»» 


» 


6 


» 


7 




» 


>» 


8 


» 


8 




n 


» 


5 


» 


9 




» 


»> 


4 


» 


10 




» 


» 


10 


»> 


11 




n 


>J 


10 


»> 


12 




» 


J» 


6 


9i 



" Nought " once. 



" Door " once. 



80 



31 



Thus out of 113 times he brought food 80 times, tea 
31 times, and the other 10 cards only twice. Moreover, 
the last time he was wrong he brought a card — namely, 
"door" — in which three letters out of four were the 
same as in " food." 
14 



280 ATTEMPTS TO CONVEY IDEAS. 

This is, of course, only a beginning, but it is, I 
venture to think, suggestive, and might be carried 
further, though the limited wants and aspirations of 
the animal constitute a great difficulty. My wife has 
a beautiful and charming collie, Patience, to whom we 
are much attached. This dog was often in the room 
when Van brought the " food " card and was rewarded 
with a piece of bread. She must have seen this thou- 
sands of times, and she begged in the usual manner, 
but never once did it occur to her to bring a card. 
She did not touch, or, indeed, even take the slightest 
notice of them. 

I then tried the following experiment :— I prepared 
six cards about ten inches by three, and coloured in 
pairs — two yellow, two blue, and two orange. I put one 
card of each colour on the floor, and then, holding up one 
of the others, endeavoured to teach Van to bring me 
the duplicate. That is to say, that if the blue was 
held up, he should fetch the corresponding colour from 
the floor ; if yellow, he should fetch the yellow, and 
so on. When he brought the wrong card he was made 
to drop it and return for another, until he brought the 
right one, when he was rewarded with a little food. 

We continued the lessons for nearly three months, 
but as a few days were missed, we may say for ten 
weeks, and yet at the end of the time I cannot say that 
Van appeared to have the least idea what was expected 
of him. It seemed a matter of pure accident which 
card he brought. There is, I believe, no reason to 
doubt that dogs can distinguish colours ; but as it was 
just possible that Van might be colour-blind, we then 
repeated the same experiment, only substituting for the 
coloured cards others marked respectively with one, 



AEITHMETICAL POWEKS OF ANIMALS. 281 

two, and three dark bands. This we continued for 
another three months, or, say, allowing for intermissions, 
ten weeks ; but, to my surprise, entirely without success, 
for we altogether failed to make Van understand what 
we wanted. I was rather disappointed at this, as, if 
it had succeeded, the plan would have opened out many 
interesting lines of inquiry. Still, in such a case one 
ought not to wish for one result more than another 
as, of course, the object of all such experiments is 
merely to elicit the truth, and our result in the present 
case, though negative, is very interesting. I do not, 
however, regard it as by any means conclusive, and 
should be glad to see it repeated. If the result proved 
to be the same, it would certainly imply very little 
power of combining even extremely simple ideas. 

Can Animals count ? 

I then endeavoured to get some insight into the 
arithmetical condition of the dog's mind. On this 
subject I have been able to find but little in any of 
the standard works on the intelligence of animals. 
Considering, however, the very limited powers of 
savage men in this respect — that no Australian 
language, for instance, contains numerals even up to 
four, no Australian being able to count his own fingers 
even on one hand — we cannot be surprised if other 
animals have made but little progress. Still, it is 
curious that so little attention should have been 
directed to this subject. Leroy, who, though he ex- 
presses the opinion that " the nature of the soul of 
animals is unimportant," was an excellent observer, 
mentions a case in which a man was anxious to shoot 



282 PREVIOUS OBSERVATIONS. 

a crow. " To deceive this suspicious bird, the plan was 
hit upon of sending two men to the watch-house, one 
of whom passed on, while the other remained ; but the 
crow counted, and kept her distance. The next day- 
three went, and again she perceived that only two 
retired. In fine, it was found necessary to send five or 
six men to the watch-house to put her out in her 
calculation. The crow, thinking that this number of 
men had passed by, lost no time in returning." From 
this he inferred that crows could count up to four. 
Lichtenberg mentions a nightingale which was said to 
count up to three. Every day he gave it three meal- 
worms, one at a time; when it had finished one it 
returned for another, but after the third it knew that 
the feast was over. I do not find that any of the recent 
works on the intelligence of animals, either Buchner, 
or Peitz, or Eomanes in either of his books, give any 
additional evidence on this part of the subject. There 
are, however, various scattered notices. 

According to my bird-nesting recollections, which I 
have refreshed by more recent experience, if a nest 
contains four eggs, one may safely be taken ; but if 
two are removed, the bird generally deserts. Here, then, 
it would seem as if we had some reason for supposing 
that there is sufficient intelligence to distinguish three 
from four. 

An interesting consideration rises also with refer- 
ence to the number of the victims allotted to each 
cell by the solitary wasps. Ammophila considers one 
large caterpillar of Noctua segetum enough ; one species 
of Eumenes supplies its young with five victims; 
one ten, another fifteen, and one even as many as 
twenty-four. The number is said to be constant in 



SUPPOSED POWEKS OF COUNTING. 283 

each species. How, then, does the insect know when her 
task is fulfilled ? Not by the cell being filled, for if 
some be removed she does not replace them. When 
she has brought her complement she considers her task 
accomplished, whether the victims are still there or 
not. How, then, does she know when she has made 
up the number twenty-four ? Perhaps it will be said 
that each species feels some mysterious and innate 
tendency to provide a certain number of victims. 
This would not under any circumstances be an ex- 
planation, nor is it in accordance with the facts. In 
the genus Eumenes the males are much smaller 
than the females. Now, in the hive bees, humble 
bees, wasps, and other insects where such a differ- 
ence occurs, but where the young are directly fed, it 
is, of course, obvious that the quantity can be pro- 
portioned to the appetite of the grub. But in insects 
with the habits of Eumenes and Ammophila the case is 
different, because the food is stored up once for all. 
Now, it is evident that if a female grub was supplied 
with only food enough for a male, she would starve to 
death ; while if a male grub were given enough for a 
female it would have too much. No such waste, how- 
ever, occurs. In some mysterious manner the mother 
knows whether the egg will produce a male or female 
grub, and apportions the quantity of food accordingly. 
She does not change the species or size of her prey ; 
but if the egg is male she supplies five, if female ten, 
victims. Does she count ? Certainly this seems very 
like a commencement of arithmetic. At the same time, 
it would be very desirable to have additional evidence 
before we can arrive at any certain conclusion. 

Considering how much has been written on instinct, 



284 MK. HUGGINS'S EXPERIMENT. 

it seems surprising that so little attention has been 
directed to this part of the subject. One would fancy 
that there ought to be no great difficulty in determining 
how far an animal can count; and whether, for in- 
stance, it could realize some very simple sum, such as 
that two and two make four. But when we come to 
consider how this is to be done, the problem ceases to 
appear so simple. We tried our dogs by putting a 
piece of bread before them, and preventing them from 
touching it until we had counted seven. To prevent 
ourselves from unintentionally giving any indication^ 
we used a metronome (the instrument used for marking 
time when practising the pianoforte), and to make the 
beats more evident w 7 e attached a slender rod to the 
pendulum. It certainly seemed as if our dogs knew 
when the moment of permission had arrived ; but their 
movement of taking the bread was scarcely so definite 
as to place the matter beyond a doubt. Moreover, 
dogs are so very quick in seizing any indication given 
them, even unintentionally, that, on the whole, the 
attempt was not satisfactory to my mind. I was the 
more discouraged from continuing the experiment in 
this manner by an account Mr. Huggins gave me of a 
very intelligent dog belonging to him. A number of 
cards were placed on the ground, numbered respectively 
1, 2, 3, and so on up to 10. A question was then asked : 
the square root of 9 or 16, or such a sum as 6 + 55 — 3. 
Mr. Huggins pointed consecutively to the cards, and 
the dog always barked when he came to the right one. 
Now, Mr. Huggins did not consciously give the dog any 
sign, yet so quick was the dog in seizing the slightest 
indication, that he was able to give the correct answer. 
" The mode of procedure is this. His master tells 



CONCLUSION. 285 

him to sit clown, and shows him a piece of cake. He is 
then questioned, and barks his answers. Say he is 
asked what is the square root of 16, or of 9 ; he will 
bark four or three times, as the case may be. Or 
such a sum as 6+1 5 2 ~ 3 he will always answer correctly. 
The piece of cake is, of course, the meed of such 
cleverness. It must not be supposed that in these 
performances any sign is consciously made by his 
questioner. None whatever. We explain the per- 
formance by supposing that he reads in his master's 
expression when he has barked rightly ; certainly he 
never takes his eyes from his master's face." * 

This observation seems to me of great interest in 
connection with the so-called " thought-reading." No 
one, I suppose, will imagine that there was in this 
case any "thought-reading" in the sense in which 
this word is generally used. Evidently " Kepler " 
seized upon some slight indication unintentionally 
given by Mr. Huggins. The observation, however, 
shows the great difficulty of the subject. 

The experiments I have made are, I feel, very 
incomplete, but I have ventured to place them on 
record, partly in hope of receiving some suggestions, 
and partly in hope of inducing others with more 
leisure and opportunity to carry on similar observa- 
tions, which I cannot but think must lead to interesting 
results. 

* M. L. Huggins, u Kepler : a Biography." 



INDEX. 



Acalles, 66 

Acanthopleura, 15, 145 

Acheta, 61, 63, 97, 117 

Acridiidse, 100, 106 

Actinia, 13 

Ageronia, 73 

Aglaura, 188 

Alciopida?, 14, 22, 137 

Aimnophila, 243, 282 

Amphibia, 32, 129 

Amphicora, 87 

Amphioxus, 129 

Angler, 186 

Anguis, 126 

Annelides, touch, 13 ; taste, 22 ; 

smell, 34 ; hearing, 87 ; sight, 134; 

problematical organs, 189 
Anobium, 67 
Anoxia, 251 
Anthidium, 71 
Anthrax, 251 
Ants, 24, 31, 43, 56, 69, 107, 115, 

178, 202 
Apion, 94 
Apis, 26, 29, 58, 69, 70, 115, 150, 

172, 194, 258, 283 
Area, 141 
Arenicola, 87 

Arithmetic of animals, 281 
Arthropods, touch, 16 ; taste, 23 ; 

smell, 35 ; hearing, 88 ; sight, 146 ; 

problematical organs, 188 
Articulata. See Annelides, Insects 



Ascidians, 129 

Asellus, 48 

Astacus, 23, 51, 88 

Asteracanthion, 133 

Asterope, 22 

Astropecten, 132 

Ateuches, 66 

Auditory hairs, 16, 79, 85, 88, 118 

organs, 77 

rods, 18, 104, 111 

B 

Balanus, 220 

Bee, hive. See Apis 

Bee, solitary, 242 

Beetles. See Coleoptera 

Bembex, 242, 246 

Birds, 129, 282 

Blatta, 46, 152 

Blethisa, 68 

Blind spot in eye, 125 

Bohemilla, 13, 134 

Bombardier beetle, 65 

Bombus, 28, 70, 73, 178, 283 

Bostrychida, 67 

Brachinus, 64, 68 

Brachyura, 90 

Butterfly. See Lepidoptera 



Calanella, 159 
Calotis, 127 
Callianassa, 50 



288 



INDEX 



Camponotus, 208 

Capitellidse, 34 

Capricorn beetle, 96 

Carcinus, 92 

Cards, Van and his, 277 

Carinaria, 87 

Caterpillars, 23, 243, 259 

Cats, 262 

Centipedes, 49, 74 

Cephalopoda, 34, 141 

Cerambyx, 67, 95, 96 

Ceratius, 186 

Ceratophyus, 68 

Chalcididse, 27 

Chalicodoma, 251, 262 

Chiasognathus, 68 

Chitons, 15, 144 

Cicadas, 61, 64, 151 

Cicadidae, 151 

Clepsine, 134 

Cockchafer. See Melolontha 

Cockroach, 46, 152 

Coelenterata, touch, 11 ; taste, 22 ; 

smell, 33 ; hearing, 82 ; sight, 131 
Coleoptera, 58, 67, 111, 151 
Collie. 280 
Color of deep-sea fish, 185 

of flowers, 199 

, sense of, 190, 194, 202, 280 

Componotus, 239 

Compound eyes, 163 

Copepoda, 48 

Copilia, 158 

Copris, 68, 95 

Corephium, 145 

Corethra, 18, 113, 117, 151 

Corixa, 75 

Corti, the organ of, 80, 105 

Corycaeus, 157 

Cossus, 148 

Count ? can animals, 281 

Crabs, 90, 92 

Crayfish. See Astacus 

Cricket. See Acheta 

Crioceris, 68 

Crow, 282 

Crustacea, touch, 16 ; taste, 23 ; 

smell, 46 ; hearing, 88 ; sight, 156 ; 

sense of color, 211 ; problematical 

organs, 188 
Crystalline cone, 166 



Culex, 68, 115 
Curculionidae, 68 
Cychrus, 68 
Cyclostoma, 140 
Cymbulia, 88 



Daphnia, 48, 206, 212 

Dead-nettle, 200 

Death-watch, 6Q 

Dias, 220 

Dinetus, 39 

Diptera, 52, 69, 110, 149, 151 

Direction, sense of, 262 

Dog, intelligence of the, 272 

Dragon-fly. See Libellula 

Dytiscus, 5, 6, 112, 131, 146, 167 



Ear. See Auditory organs 

in tail of JSIysis, 92 

, structure of the human, 78, 101 

Earthworms, 206 
Elaphrus, 68 
Elaterida, 67 
Empusa, 176 
Endosmosis, 25 
Englena, 130 
Epeira, 146 
Ephippigera, 103 
Epithelial cells, 14, 20 
Epithelium, 11, 19 
Eristalis, 69, 174, 176 
Eucopidae, 85 
Eucorybar, 74 
Eumenes, 245, 282 
Euphausia, 161 
Eurycopa, 189 
Eutima, 83 
Evaneadae, 27 
Eye, compound, 163 

of man, 121 

, pineal, 126 

, simple, 170 



F 



Fish, 182 
Flowers, 200 



INDEX. 



289 



Fly. See Musca 
Forficula, 151, 167 
Formica. See Ants 



G 

Gammarus, 49, 188 
Gasteropods, 86 
Geotrupes, 68 
Geryonia, 86 
Glomeris, 50 

Glossopharyngeal nerves, 19 
Gnat, 68, 115 
Gryllotalpa, 102 
Gryllus, 63, 98, 106, 108 

H 

Hairs, auditory, 16, 79, 85, 88, 116 

, depressed, 17 

, flattened, 56 

— , glandular, 29 

, hollow, 17 

in insects, 16 

of touch. See Tactile 

, olfactory, 16, 25 

, ordinary surface, 16, 56 

— , plumose natatory, 16, 94 

, simple, 18 

, solid, 17, 82 

, tactile, 16, 18, 28, 29, 56 

, taste, 16, 28 

Haliotis, 5, 139 

Hattaria, 127 

Hearing, organs of, in Vertebrata, 77 ; 

Ccelenterata, 82 ; Mollusca, 86 ; 

Annelida, 87 ; Arthropods, 88 

. , sense of, 60, 97 

Helix, 14, 139 

Hemiptera, 112, 151 

Hesione, 135 

Humble-bee. See Bombus 

Hydaticus, 40 

Hydrachna, 28 

Hydromedusae, 86 

Hydrophilus, 168 

Hydrozoa, 13 

Hylceus, 58 

Hymenoptera, 23, 25, 56, 57, 58, 69, 

70, 96, 151, 181, 250 



Hyperia, 171 
Hypoderm, 5, 1G 



Ichneumon, 54, 58 

Ichthyosaurus, 129 

Infusoria, 11 

Insects, touch, 16 ; taste, 23 ; smell, 

35, 52 ; hearing, 61, 94 ; sight, 

146 ; problematical organs, 188 
Instinct — 

Ant, 202, 232, 267 

Bee, hive, 194, 253 

, solitary, 255, 260, 262 

Birds, 282 

Bombardier beetle, 64 

Change in, 244 

Crustacea, 90 

Daphnia, 229 

Dog, 272 

Fish, 186 

Fly, 174, 177 

Limitation of, 253 

Of direction, 262 

Onchidium, 144 

Paussus, 65 

Wasp, solitary, 243, 282 
Isopteryx, 109 



Jelly-fish. 
Julus, 49 



See Medusa? 



Labyrinthodons, 129 

Lacerta, 126, 128 

Lamellibranchiata, 14, 141 

Lamellicornia, 37, 52 

Lamium, 200 

Lampyris, 167 

Lancelet, 129 

Lasius. See Ants 

Laura Bridgman, 273 

Leech, 189 

Lema, 68 

Lepidoptera, 37, 71, 94, 111, 148, 

151, 168, 181 
Leptodora, 156 



290 



INDEX. 



Leucospis, 251 

Libellula, 69, 70, 149, 152, 171 

Light-organs, 161, 185 

Ligia, 167 

Limitation of instinct, 253 

Limpet, 4, 138 

Linmlus, 159 

Lithobius, 155 

Lizzia, 132 

Lobster, 90, 91 

Locusts, 62, 99, 106, 111, 149, 176 

Longicorn beetles, 66, 95 

Lucanus, 43, 52 

Lucilia, 177 

Lycosa, 179 

Lyda, 58 

M 

Mammals, 129 

Maxillae, 25 

Meconema, 102, 105 

Medusae, 6, 22, 82, 83, 84, 85, 86, 

117 
Meissner's corpuscles, 7 
Melolontha, 52, 58, 67, 68, 148, 152, 

168 
Mesonotum, 67 
Metronome, 284 
Miltogramma, 254 
Mollusca, 14, 22, 34, 61, 86, 120, 

137, 140 
Mordella, 148 
Mosaic vision, 163 
Mosquito. See Culex 
Moths. See Lepidoptera 
Murex, 139 
Musca, 17, 29, 30, 45, 53, 58, 68, 71, 

110, 113, 148, 153, 165, 172, 174, 

177, 254 
Mutilla, 69, 70 
Myriapods, 155, 205 
Myrmica. See Ants 
Mysis, 92, 98, 157, 161 

N 

Nautilus, 140 
Necrophorus, 66 y 68 
Needle cells, 21 
Nematocera, 151 



Nematocysts, 12 
Nereis, 12, 135 
Nesticus, 180 
Neuroptera, 111, 151 
Newts, 207 
Noctua, 73, 243, 282 



Oceanidae, 86 

Ocypoda, 61 

Odynerus, 247 

CEstrus, 148 

Olfactory organs. See Organs of 

smell 
Omaloplia, 68 
Onchidium, 14, 131, 143 
Oniscoidse, 170 
Ontorchis, 6, 84 
Organs of hearing, 17, 19, 77, 81, 93, 

109, 114 

of sight, 19, 130, 146 

of smell, 17, 88 

of taste, 17, 19, 21 

of temperature, 6, 10 

of touch, 11, 14, 17, 19, 131 

, problematical, 182 

Origin of organs of sense, 3 
Orthoptera, 37, 99, 107, 112, 131, 

176 
Oryctes, 68 
Osmia, 251 
Otolithes, 52, 82, 84, 85, 89, 90, 91, 

92 
, possible origin of, 3 



Pacinian corpuscle, 8 

Pagurus, 51 

Palasmon, 51 

Palinurus, 61 

Palpi, 30, 37, 38, 39, 41, 73 

Paludina, 140 

Pamphila, 184 

Paniscus, 58 

Patella, 138, 140 

Paussus, 65 

Pectens, 61, 141 

Pectunculus, 141 

Pelagia, 86 



INDEX. 



291 



Pelobius, 68 
Periplaneta, 152 
Perophthalmus, 144 
Pheidole, 108 
Phialidium, 85 
Photichthys, 185 
Pineal eye, 127 
Pinnotheres, 51 
Piscicola, 134 
Platyarthrus, 207 
Plesiosaurus, 129 
Pleuromona, 189 
Podophthalinata, 50, 156 
Polydesmus, 189 
Polyophthalmus, 33, 98, 134 
Pompilus, 58 
Ponera, 69 
Pontella, 47, 48 
Pontinia, 51 
Poodle dog, 276 
Pressure-point, 10 
Prionus, 67 
Proctotrupidae, 27 
Pronotum, 67 
Prosobranchiata, 138 
Protoplasm, 21 
Protozoa, 32, 61 
Pteropods, 87 
Ptychoptera, 113 

E 

Recognition among ants, 234 

Eeptilia, 127, 130 

Respiration in insects, 35 

Retina, 123 

Rhopalonema, 85 

Rods, auditory, 18, 104, 111, 187 

, olfactory, 55 

, retinal, 124 



s 

Salivary gland, 30 
Sarcophaga, 111 
Schizochiton, 145 
Scolopendra, 155 
Scopelus, 186 
Scorpions, 179 
Sea-anemone, 12, 187 



Sense-hairs. See Hairs 

Sense of direction, 262 

Sense-organs, origin of, 3, 86, 111 

Senses, unknown, 192 

Serolis, 189 

Setae. See Hairs 

Sex, power of regulating, 262 

Sight, organs of, in Vertebrata, 121; 
Ccelenterata, 131 ; Annelida, 133 ; 
Mollusca, 137 ; Arthropods, 146 

, sense of, 118 

, three possible modes of, 118 

Silpha, 38, 41 

Si rex, 58 

Skin, termination of nerves in, 18 

Smell, organs of, in Vertebrata, 32 ; 
Protozoa, 33 ; Ccelenterata, 33 ; 
Annelida, 
pods, 35 

Smerinthus, 73 

Solaster, 133 

Sound, organs of, not known in Pro- 
tozoa or Ccelenterata, 61; Mollusca, 
61 ; Crustacea, 61 ; Insects, 62 

Sphex, 245 

Sphinx, 73, 148 

Sphcerotherium, 74 

Spiders, 74, 146, 155, 170, 178 

Spondylis, 67, 141 

Squilla, 51 

Stag-beetle, 43, 52 

Staphylinus, 50 

Stenobothrus, 62, 63 

Stratiomys, 167 

Syrphus, 69, 170 



Tachytes, 246 

Taste, organs of, in Vertebrata, 19; 
Annelida, 22 ; Mollusca, 22 ; Ar- 
thropods, 23 

Telephorus, 112 

Temperature, organs of, 10 

Tenebrionida, 68 

Tenthredo, 27, 58 

Theridium, 75 

Touch, organs of, in Vertebrata, 7 ; 
Protozoa, 11 ; Ccelenterata, 11 ; 
Medusae, 12 ; Annelida, 13 ; Mol- 
lusca, 14; Arthropods, 16 



292 



INDEX. 



Touch, sense of, 7 
Tracheae, 29, 30, 101 
Trachyrnedusae, 85 
Trachynemadaa, 1S7 
Tritonia, 87 
Trochus, 138 
Trox, 68 
Tunicata, 129 
Turbellaria, 133 



Van, 276 
Vanessa, 73, 174 



Varanus, 127 
Vaterian corpuscles, 7 
Vertebrata, 7, 19, 32, 77 
Vespa, 28, 55, 58, 175, 178, 283 

W 

"Wagner's corpuscles, 7 
Warmth organs, 6, 10 
Wasp. See Vespa 

, solitary, 242, 282 

Weevils, 67, 94 
Wolffian glands, 27 
Worms. See Annelide-3 



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